[jermasaurus]

I believe the computer should be the same, but you will need a chip for the 305 motor.

The motor is the same bolt pattern, but you may have an issue with the pilot bushing in the crank. I heard the crank from an auto won't have the provision for the bushing.

motor mounts should either be the same, or an easy swap. A 4.3 is kind of like a small block missing the front two cylinders. Might be the only 6 cyl or one of the few with the same bolt pattern as a small block.

The fuel system should work as far as the tanks, pumps, and i think the Injectors themselves.

I had an 87 Monte Carlo that was originally a 4.3 tbi (only motor with fuel injection in a Monte back then) It had a 305 dropped in its place and used the same ECM and wiring for the most part. It was cool because not many others had a fuel injected v8 in one of those, and it fast passed emissions while still testing as a 6 cyl.

I did have an issue with overheating occasionally on a hot day with the a/c on in stop and go traffic. It was the 4.3's radiator with an electric fan. So it may be worth swapping that

Good luck. Should be a nice swap.

-Jeremy