Bax, if you do a search on "1986 donor" (make sure you search "Let's Build It" and not just "Roadster Grandstand") you will find that this has been discussed extensively on the forum. There are some major differences between the 1986 and the later cars, including:
smaller brakes, different front spindles, speed density and not mass air, smaller rear-end (7.5 instead of 8.8), smaller throttle body (58 vs 60mm), terrible heads, non-HO motor (crappy pistons), and some other less important stuff. Many people have used 86 donors and most say they regret it as they wind up throwing out the 86 gear for better stuff anyway.
I used an 86 donor and I have had to change a few things. The rear IS 8.8 but the front spindles are different. The spindles can be used but according to FFR they have to be modified to work. I just bought some different used ones. The E-brake handle is different but the way it is setup allows you to put it next to the drivers seat (I hope, Im not quite done). Yes the pistons and head suck but I rebuilt the motor and changed those parts. Most everything else is the same. The gas tank fit but the straps were wrong, one was to long and the other was to short. I went carb so I did not need any of the speed density stuff.
You should be able to use the gas tank and shroud, steering column, brake line brackets, front lower control arms, rear control arms, rear axle if its a 8.8. 7.5 axle will fit also if you dont want build the motor too much. tranny should work, master cylinder, pedal box, gas pedal. Spindles will work if you remove the shims on one side of the FFR piece. Modify the brake pedal and the brakes will work just fine. If you have the smaller diameter brake booster plan on making it fit with a small frame mod. Rear springs will work, Rack and pinion will work, 20 to 1 ratio but great for the street. If your handy with a welder, you can make adjustable seat sliders with the stock ones. Overflow bottle will work mounted to the X-member, radiator will work also, along with the drive shaft. Get the gas filter bracket also. All I can think of at this time
I agree with Scott. I used a carbed 1985 as a donor. The engine worked great as the '85 doesn't have the weird pistons/head combo the '86 does. I did get sn95 spindles and brakes and a T-bird rear axle. I guess it comes down to how much extra fiddling around you want to do. The '85 worked out to be a nice carbed donor, I'm not sure the '86 would be as easy.
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