Honsetly, I like the look of the 5th gen better. Plus I've already got money into the body of my car so I really don't want to start all over.
You're right, the 3rd gen engine uses only a MAP sensor, no MAF to deal with. I got the engine from japan motor here in Montreal. They didn't know what it was so they gave it to me for ALOT less than it is worth.
Right now I'm going to use the stock s53 tranny from my GTS. I know some guys running this set up in the states and it works as long as you don't abuse it. Once the summer comes I'll probably swap in an MR2T transmission (hopefully the one with an LSD). Ideally I'd like to wait and do it right the first time but the engine in my car now is about to die and I really need a vehicle so I'll just take it easy for the first few months.
Cheers