u can use any 3SGTE engine ( motor, long block only ) in an MR2 but the problem start with the harness
good luck getting a 5th gen 3sgte .... i been looking for 1 and i only got able to the 4th
4th gen 3sgte with a 3rd gen harness ...runs ok ... for stock .. really good and for the price even better ...

good luck with the project

martin