66 dart rear end swap

Since your car should be the small bolt pattern lug size, I would seek out a small bolt 8 3/4” rear, unless you plan on changing the front to large bolt. The 8 1/4” A body unto will also bolt right in place, but uses the large bolt pattern, as does the 8.8” Ford unit, which will need one side of the axle tube cut, as one tube is longer than the other and the center is offset. You would also need another short side axle to replace the longer one. It may cost more to purchase an 8 3/4” A body rearend, but in the long run, it’s easier to work with, and it’s a bolt in. For any of these 3 swaps, you will need to have your driveshaft shortened as well!