I've got almost the same question if someone could help me out please.

I've also got a 99 GTP but it's my trans that's bad, the motor is still good but has high miles, 200k. I was planning to have the trans rebuilt soon.

I also want to do some mods to the engine, headers, tune etc etc 3.4 pulley. Of course I'm a little concerned about trying to mod a motor with this many miles on it. I'm sure I'd be rebuilding it soon too if I do. I've read a little about swapping to a genV supercharger, and was curious if I could just get a junk yard engine/tranny with fewer miles from an 04+ and swap them both in at the same time? That way I'd have a better engine with fewer miles, and tranny too.

So from what I've read above, I could swap engines but I'd need a throttle body adapter of some sort. As far as the tranny goes, it's either not bolt in or not plug and play, or both? Does anybody have any links?