I have done a couple or 3 diff swaps, i dont think its that much work. About the same amount of time to overhaul a diff if its not blowed up. I have a buddy that does my driveshaft work,cheap.
Swapping a complete rear vs wheels....is still more work lol. The OP wants to get rid of the 7 1/4 anyways and I did the same with my 66 /6 B body so it wasn't hard to do but was still more work than doing a wheel swap :D