Hey, before you do anything as serious as an engine swap, ask yourself what you want out of this car. If you want a track/fun car for the turns with decent power, then IMO you certainly do-notdo not want to put in a MKII motor, as that it will ofset the balance of the car.
The problem of course with turboing a 4A-GE or one of its variants (or even the MKII turbo motors) is of course the dreaded phenomena of "turbo lag", that is, the delay between you hitting the gas, and the turbos spooling up.
I don't mean to offend any of the MKIIers around her, but look how ferrari, lamborghini, the top of the line porsche (Carrera GT), McLaren F1, etc, all do their motors. Not a single of of them is a turbo (or any sort of forced induction for that matter)
If i wanted straightline speed, id do a engine swap, but in a big turbo, a huge wing, really big tires in the back, and small ones in the front, but thats not what i'm looking for, and IMO, thats not what the MR2 was designed to do.
I like the 4A-GZE, because there is absolutely zero lag, at least none that I can detect. It has a clutched supercharger too, which means it only engages when you want it to.
Many people/compaines lessen the lag using a twin turbo system, or even four turbochargers.... but I do not believe that you can fit two in the engine bay, and even if you did, i don't think that the engine can push out enough air to spool them efficiently.
So...in conclusion, I personally wouldnt turbo your motor, or put one in thats not meant for an AW11, but if you really want to go fast in a straight line, then put in the MKII motor.
Oh, and finally, the turbo motor will make the car faster, but a properly modified 4A-GZE will be pretty close behind...and if you ask me, will be laps ahead of the other guy at the track.