And if you a get a JDM 20V, you'll just scratch your head.
Why would you want a 4A-FE? The difference is in the head... Yamaha helped build the G heads. FE is good for less power. Better milage though. It will built to the tranny from what I understand.
FE's don't have the T-VIS system, run on a different ECU, are fuel injected. Take note, the 4A-GE's are all fuel injected... All 4A and up are from the best of my knowledge...
The GZE will not just fall in the car. Unless it has one to begin with

Sure some other stuff needs to be worked on. And you would need the transmission, since supercharged used a different tranny.
The engines in the Corolla GT-S and Geo Prism GSi are 4A-GE's. They also use the same Tranny as the 87-89 MR2.. the C52. However, you cannot use a tranny out of a FWD 4A car, as the linkage's are on the other side for shifter.
Just get a 4A-GE if you feel hte need to swap... will be cheaper as you won't need to get the ECU and other crap to deal with for the other engine options.
BTW, how many miles are on this MR2? And what year is it?