Stock FETs
 

Theory:
Take Stock FETs from a used Supra its dead due to frieded Reciever. and put them on a new one???

That would just allow more voltage through the existing circuitry.
Nothing wrong, as far as I know. Not that I would.

Well wouldnt more voltage mean more Power

after my civic died on the operating table it became a donor for lots of parts the mosfets was one of them.I did this upgrade last night I gotta say I was impressed with the results. more power but not a lot but enough to almost make your tires come off like the 6 cell mod would but with only 4 cell instead. if you got the patience I say go for it.

Ok im trying this tommorrow with a 6 Cell Upgrade. Also does anyone know of a small RF thing that would allow me to turn off and on the 5th and 6th Battery

Wire them in parallel with the motor, putting a switch on each, and maybe a 'master' switch in series with the whole thing, so you could turn them both on at once immediately (although that's really not necessary, and there's not much room for wires under there).