Welcome aboard!!

Since the tcase is divorced...there is a driveshaft between the tranny and tcase, any tranny will work...and the combo you listed has been done.
On gears, Randys ring and pinion can set you up...tell them its an M715...they got it...you are gonna be looking at 4.56 gears...thats the lowest numerical gear the stock setup can use.
brute4c