It is the same motor just with the california emissions package like 91MR2quickNA said.
The 20V motors came in different variations just the 4age motors. They produce anywhere from approx. 170-190 hp. Since this was a japan only motor all the parts will be needed to be traced from there or someone that knows about them. You will be able to find a good deal of parts for the 4age and the AW11 MR2 is a great handling car.
For more information you should check out
www.Club4ag.com
Or if you are looking for some racing parts try
www.todaracing.com