Alternate engines for Porsche 944S?

Easy: 944 8v non turbo. Difficult: a 944 turbo engine or 968 engine Really difficult: There are kits available for small block Chevys sold by a few different vendors. Check out Renegade Hybrids first. I have personally been waiting to see someone go with the GM 3800 supercharged, but it remains to be seen.

To expand on your other question, you can find kits to bolt a small block into your car. The 944 motors are all aluminum and unless you find an aluminum small block, you're going to have to bulk up your front struts. You can probably drop an 8-valve 944 motor in your car anything from '83-'88 should work as long as its a 2.5L and you use the right injectors, AFM and I'm drawing a blank on the other sensor you need to match to the motor. You would honestly be better buying a different car rather than spending all your money fixing this one.