people like the OP is looking at the car like a sandwich - he thinks the car shell is the bread and the engine etc are the fillings.
I find such projects from such people very relaxing - because after all the millions spent on it - they end up as a disaster and then rot in the scrapyard. Its comedy gold to be honest. - the 2JZ is an ancient engine now, very dirty and requires very high rpm to deliver power, the 2GR is a better choice but again - the cost will shoot twentyfold in finding a 2GR and somehow mating it to the mazda box.
What people dont understand is that the RX8 is basically a sort of mid engine car, the engine sits behind the front axle and is built to be raced on a track - not on dragrace (which is the only sport Pakistani bourgeoisie people know)