Just buy a conversion kit and slap in a steelcase supra 5 speed, (great for wheelspin!!!)
Too many questions, none of which seem specific to me, sorry JJ.
Although I do not believe that a 4.44 'diff conversion', (if that's what you're thinking of doing?), would 'plug and play', there are calibrations in the TCU for speed semsors etc which control gear changes etc, I don't 'think' it would work 'that easy'
Sorry
Sixpack