8.75 A body U joints?

If the axle is original, its most likely the 7.25" axle. I say this because I think the 8.25" came out in 1972, as a replacement for the 8.75" If the axle is the 7.25", you'll need a ujoint with two sizes, which TRW makes. I don't know the PN offhand, but I do know I have one under my 72 Dart. I swapped from the 7.25" to the 8.75" axle. You'll also need to shorten the driveshaft.