first gen rally road car.

[Whizbang]

the subframe from a Turbo II is the same as a GXL and very similar to basically everything else barring an FC marque.

As far a the engine goes. I love NA engines for their simplicity, low cost effectiveness and the high reliability. Plus in rallycross, you'll basically have no need for turbos. You will barely be able to build boost before your off the throttle again. So 13B NA is a good choice.

Since you have an 84, find yourself the Kia Sportage 4.77 gears first and foremost. Should be inexpensive (~100 dollars). Find a good Clutch LSD (FB or FC or miata) as well.

As for the engine. A good four port (ie turbo II) engine is best for making some good NA power. The porting is up to you and your driving preferences.