Will any 8 3/4 fit???

You can use off the shelf axle shafts if you have it narrowed correctly, so if you have it cut to a body width you would need a body shafts,
What kind of car is it going in? Street? Strip? Full restoration? It will cost you an arm and a leg to have it narrowed, get axle shafts, add a sure grip, rebuild the brakes, rebuild the center section. May be a better choice to use a dufferent axle thats ready to go like an 8 1/4 or even the ford 8.8