I have to agree with Rusty, the whole car will need to be built around the transmission layout. Apart from strength and suitable ratios, do not underestimate the difficulties of getting the gear linkages forward around the engine in a mid engined car. A crappy gear change that cannot be improved will spoil an otherwise excellent car.
alfonso wrote:so if i find a wrecked 2007 jeep gran cherokee srt8 4x4
move drive train to rear with tranny in back facing normally to front
This is definitely the best way to go IMHO, if your budget is limited. It would use mostly all the original readily available parts, with minimum problems. It is then just a case of turning the whole diff housing upside down to reverse the rotation of the axles. Either mid engined RWD or full 4WD should then be fairly easy.
Doing it this way places the gearbox in the middle of the car, with all the engine accessories accessible at the rear. A conventional rear gearbox mid engined car will have the fan belt, water pimp, alternator and most other things buried deep near the middle of the car. Not so convenient.
Cheers, Tony.