Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.
your car is screaming V6 conversion!!
you may find the gearbox of the 3S-GE will fit the 3S-GTE, get your self on google and search MR-2 turbo conversion! im sure there will be heaps of stuff about it.
you can change the gearbox with the engine in 110% definite on that as i have done it twice when changing clutches
So if anyone tells you it is not possible tell them b.s!