8.75 A body U joints?

My suggestion, if you want to move the rear back, do it at the spring mounting brackets, not at the perches. Get a 1/2" block of aluminum and put it between the front mount bracket and frame.

Getting a 30" tire on a Dart is a chore if you don't either move the rear at least 1" or section the front wheel lip.

I put 28" on them before in the stock location. you may have to beat the front lip in a bit if sectioning isn't your thing.

Most likely a 741 case will have a 7260 u joint, the same as the 7 1/4. Even if it's the larger 7290 joint, ther is a conversion joint available. Spicer 5-527x, IIRC.