I have a 1986 NA with a 170K+ blown engine. I have been out of it a while and really can't remember...

Can I put a S5 NA into it if I can find a used one?

Weren't the intake ports or something different?

 

You can, with a couple of minor modifications. You'd want to reuse your wiring/electronics/sensors/TB. You can run the S5 NA intake manifold, which is better than the S4. You'd probably wind up forfeiting emissions stuff if you did. You'll have to make a minor wiring plug change to the rear iron coolant temp sensor. You'll have to either delete the OMP and run premix, OR swap on an S4 front cover so you can retain your OMP. The front cover swap can be tricky and dangerous if you don't know what you're doing, so I would recommend that you only do that if you are experienced or very good at following instructions. If you buy something from me, I can set it up for you in advance.

You need to run the flywheel that matches the rotors/rotating assembly. Everything clutch-back can stay S4.