Putting a late model 8 1/4 Jeep rear end in a 66 Dart

Hello,
I have heard / read that you can put a late model Jeep Cherokee 8 1/4 3.55 rear end in the older A Bodies...
Has anyone done this? Seems like a great way to get rear disc brakes, an upgrade from the 7 1/4 rear in there now and move up to the 5x4.5 bolt pattern.
What am I missing?
Thoughts?