Save the motor mounts, V8 steering center link, exhaust manifolds, gas pedal and throttle cable assembly. The only body modification you might have to make is notching the torsion bar crossmember on the passenger side if you want true dual exhaust. You can do dual exhaust without doing that, but the pipe hangs lower to get under the crossmember. Find a later 904/998/999 and your driveshaft will work right back. You might have to modify your existing shift linkage from the slant trans. One more thing to watch for if you swap to a later 318 and use the 65 exhaust manifolds. Mock up the drivers side manifold to the motor before you put it in the car. The early A drivers side manifold will hit a bump on the bottom of the later heads. It's a danged if you do, danged if you don't situation. If you grind the slightest bit too much on the head bump, you hit water. If you try to tighten it without good clearance, you will crack the manifold. It's fixable with conservative grinding and double gaskets, or no grinding and a spacer between the manifold and head. Good luck with it!
