Prior to stretching the frame, you will need to loosen or remove the radiator hoses, unhook the shifting cables, fuel line, brake line and the wires that are attached to the firewall that do not have sufficient length to be moved back 11 inches. If you have not removed the battery, you will need to do so at this point. The cut will actually go through the current location of the battery. 
Preparation for cutting
It is very important that you have a level surface to work on for this next step. Place the car on blocks and use shims to level the car across the front as well as along the door frames. Be sure to support the front half of the car in such a manner that when you finish the cuts that the front will still be supported. Use masking tape or duct tape to mark the frame 5 inches back from the firewall where you plan to cut. This works better than trying to draw a scribed line on the frame. 
You will cut the cradle at a location 1.5 inches back from the point where it attaches to the section next to the firewall. 
Once the car is fully supported, place a floor jack under the back half of the car beneath the support that runs under the engine. Cut through the first two frame pieces on each side.   Then cut through the cradle section. Once the car is sectioned move the back half away using the floor jack. Insert the 11 inch spacers starting on the top rail. 
Tack weld the extension brackets in place. Continue to check the level both across the car as well lengthwise. 
Check for square by using diagonal measurements. A good measurement is from the edge of the rear strut support to where the firewall meets the frame. 
Measuring to check for square 
When you are done welding the 2 square tube, you will then weld the flat bar on the opposite side to provide additional structural support.
I have had multiple questions about the rack that was built to lift the car.  It consists of 2 - 2x8x16ft for the top rail. These were fastened to 4x4x7'6" posts with casters on the bottom. I used 2x8x7ft across the front and back on the top and bottom. I used 2x4 angle braces from the post to the 2x8s. I placed a 2x8 above the wheel wells over both the front and the rear wheels. I installed pulleys in the 2x8s over the wheel wells. I used a come along attached to the ropes that allow me to lift the front and back together or separately.  You do need to make sure that your garage has the clearance to move past the garage door opener as well as allow the doors to close. I have about 1/2" clearance from the opener and about 2" from the door. It's tight but I can do it without any assistance.
In order for the firewall to match up to the rear window on the roadster, it is necessary to move the firewall forward 3".  This is accomplished by cutting on either side next to the frame and simply puling the firewall forward.  This is not necessary on the VT or SE. To anchor the firewall I used 1x2 tube that I welded on top of the frame. I then welded a small section perpendicular to the firewall and welded this to a piece fastened to the top of the firewall. Because the firewall metal is very thin and I welded flanges on either side of the 1x2 to straddle the firewall for additional support.
The front hinges will rest on a bracket that is fabricated from 1x3 inch tube with a piece of 3/8 inch flat bar welded to the top.  This piece is challenging to get welded in place. It is attached directly to the frame. The section on the other side next to the brake cylinder is really challenging as there is little room. (You will notice that there are no close-ups of these welds)
There have been some questions on the possibility of removing the gas tank with the subframe installed. I need to remove the tank to install a high capacity fuel pump. I made this discovery after I had already welded the subframe inplace.  By cutting a section from the subframe and removing the sheetmetal directly in back of the tank, it is possible to remove the brackets and pull the tank out. I welded plates on either side of the section that I removed and then drilled through the plates and subframe. I will bolt this piece back in place when I replace the gas tank.
There have been some questions on the possibility of removing the gas tank with the subframe installed. I need to remove the tank to install a high capacity fuel pump. I made this discovery after I had already welded the subframe inplace.  By cutting a section from the subframe and removing the sheetmetal directly in back of the tank, it is possible to remove the brackets and pull the tank out. I welded plates on either side of the section that I removed and then drilled through the plates and subframe. I will bolt this piece back in place when I replace the gas tank
I got the linkage connected. It involved threading the ends of the Northstar cable and the Fiero cable. I used the rods supplied by IFG to tie the two together. I can now shift gears from inside the car.. Cool......
I added the diagonal braces from the stretch to the bottom of the door. I used 2" tube. This should provide an extra bit of rigidity to the car.
I can now drive my car!
I was able to get brakes hooked up and with the adapters, I could mount my wheels. This is the way my Friday went just to give you an idea what kit car builders go through. I had the 6000 spindles, but was missing two bolts and one axle nut (dealer items). I went to the dealer and was able to pick them up. They had to be ordered last week. I returned the Alante Rotors because they were vented and would not go with the 88 Buick Riviera calipers. I got Pontiac 6000 STE (four wheel disk version) rotors that would fit the Alante Hubs. I took back the Riviera rotors and went with the Pontiac 6000 STE calipers because they would accommodate the Fiero brake cable. Got the rotors installed and went to figure out how to mount the calipers and found out the guide pins were wrong size. It looked like I would have to fabricate a bracket. (I'm getting good at fabricating things by now) Went to wrecking yard to see if they had any brackets that could be adapted to fit. Two wrecking yards later, I decided to go the the dealer. He was out of stock. Decided to try O'Riley's auto parts. They had guide pins but they wouldn't fit my calipers. I went to Van's Auto parts where I bought the 6000 STE calipers and they told me that the calipers that I had in hand were for a 4 wheel drive Pontiac. The guide pins were correct, the calipers were wrong. The main store down town had the correct calipers and they were open till 8:00. I took the 4 wheel drive versions back and got two Pontiac 6000 STE rear calipers and headed home. They bolted directly to the 6000 spindles. Guide pins were included with the calipers. I went to supper and on the way back decided that I should replace my rear hoses with new ones. O'Rileys was still open and were out of stock but the other store had two and could have them by 9:30 Saturday morning. Done deal. Went home dreaming of driving my car on Saturday. Saturday morning up early, removed old hoses, Bolted on last caliper about time Frank arrived. I needed to move two of the boot clamps on the Northstar axle out a little as the boot was pinching because the shaft had been shortened. Frank did that while I removed the emergency brake mechanism from the 84 calipers. Oh, by the way. The Pontiac 6000 STE calipers are exactly the same as on an 84 Fiero caliper. This was good because I could now get back my $110 core charge. By now its 9:30, call O'Rileys, hoses aren't in, should be in by 12:30. Meantime, I can't get emergency brake brackets our because the star bolts won't break loose. Drill them out, get the brackets but now I need some bolts to hold the emergency brake bracket to the caliper. Frank and I head to Van's to see if they have bolts and get another star socket and brake bleeding kit and turn in the Fiero cores to get my $110. No bolts at Vans, head to O'Rileys. Hoses are in, no bolts. Stop at ACE hardware and they have bolts that will work. Progress. Head home, hook up hoses, Frank attaches hose to first caliper and the calipers threads are stripped and won't hold the hose bolt. Pull the caliper, head back to Vans to see if I can get my 84 core back so I can at least hook up the brakes. They still have my core, they order new caliper from other store which will be in on Monday. Head back home, Frank has got the other brake line connected to caliper, hook up old 84 Fiero caliper and new hose. Bleed brakes. Throw in old seat. Start car, back out of driveway. Test brakes. Frank gets in and we head down the street. I guess now is the time to see what this Northstar will do so I punch it a little. WOW. So now I decide to really hit it. MY GOD! This is probably more car than I have ever driven. It will set you back in your seat and get your adrenaline going. Sunday I put in one of the leather seats for a trial fit.
I added a brace in front of the rear radiators. I will tie in the radiator frame with a strap ( yet to be installed) as indicated where the yellow lines are
I started fabricating the plate to hold the shock bracket. The first picture is the plate welded to the angle iron. The second picture is the plate positioned inside the wheel well. I have not drilled the holes yet for the shock bracket. The third picture is the bracket clamped to the side of the dash where it will be welded. These pictures are on the passenger side.
Here are the openings and the bolt holes that have been drilled. You can see where the coating was removed inside the bezel to epoxy the bolts in. I sprayed the outside with primer and will paint them a candy apple red with clear coat when I am done.
I attached 1" square tube to the inside of the car that will be used to attach the edge of the car to the rail along the bottom of the car. I did not cover the rod in all places as I will be welding pieces to it when attaching it to the car.
I attached a 1" square tube from the center to the side wall to give the edge more rigidity. I notched the frame to accommodate the 300ZX headlights. I filled in the area with plate steel. I built a frame to support the front of the spare tire area that will also act as an anchor for the straps that cover the radiator.
I filled in the original round opening that I had cut for the gas tank and created the new opening in a better position to accept the filler component off of the Fiero. This week I glassed the inside with mat. I used epoxy to attach the fiberglass cutout to the Fiero gas cap.
Because my roadster was one of the first ones built, IFG has made several improvements in the later models. The new roof section has a arc that matches the inside of the roof panel and a slight backward slope.  Ray sent me the new section and I cut it in and added a new steel section which I will glass in. I left the steel under the old section until the new piece was glassed in and then I cut out the old bar and replaced it with a 1" tube that I bent to match the roof line.
I got the gas cap door working. I still need to finish the inside area. The area to the left of the cap is where I had cut the opening in the wrong place the first time.
I made a 1" square tube frame to go along the bottom of the front bumper. I will attempt to tie this into the frame once the car is finally mounted.
I painted the trunk area and removed all the water pipes and painted them blue to match the motor area.
I took a few shots as a refresher now that the body prep is nearing completion. 
I got a rod kit from Jegs and made a strut brace for the rear struts.
I made necessary changes to the door to fit my modifications of narrowing the door. I test fitted the weatherstripping to make sure I got a good fit. I then installed the rocker pannels by pop riviting them in at the bas and then glassing the top edge to the inside door lip. 
Beginning the sanding process. I used masking tape along the body line and sanded with 80 grit sandpaper to the edge of the tape, moved the tape to the sanded line and then sanded the other body panel. This will help define the line when painted. My wife Cheryl is helping out with the sanding and keeping me going. I can't tell you how important it is to have a partner who is supportive of your project. I am very lucky.
Installed the motorized antenna. It automatically retracts when power is turned off. If will not interfere with the roof pannel and it just seamed like a good place to put it.
Built a bracket to cover the wiring and hoses next to the firewall. I actually installed one more brace not shown where it angles down. I then cut sheet metal to fit around the wires and hoses and painted to match the rest of the interior panels.