My .02, 4200
You may have to use a different trans depending on how hot you make the engine (sounds like you will) but the 4L65E that comes with the engine (ie no adapters) should last till you do.
Cheapest way (in the long run) will be to buy a wrecked Trailblazer, Envoy, etc if you plan to run the factory computer.
If you plan to run aftermarket (ie Megasquirt like efi-diy has) that's not particularly important.
Sounds like a neat project, mine (4200) is a '50 Jimmy I'm hopefully going to be able to go through with my pops (we both have projects we have to get through first, and he's not getting any younger, I sure hope we get to it).
Good luck.
Just out of curiosity what are you hearing that's "bad" about the 302 (aside from it's the wrong vintage for your car)?
