front end swapped to disks, what axles do i need to swap in so my lug patterns match?

Oklacarcollecto said
They never made a 7 1/4 in BBP from the factory that I am aware of. The 73 - 76 7 1/4 rearends were still SBP and had drum brakes on all 4 corners but the cars with disc brakes had 8 1/4 BBP rear ends. 1972 was the last of the 8 3/4 rearends in an a body.

They did build train car loads of 7.25 rears with large bolt pattern from 1973 up. I own 2 of them. There are other differences in them besides the bolt pattern though. The axles and wheel bearings are installed differently.