Help with rear wheel cylinders

Pretty much all of the LBP drum rear brakes used 15/16" wheel cylinders. The only difference over the years was a change to the thread size of the bolts, 3/8-24 to 7/16-24. The wheel cylinders are functionally the same otherwise, and some manufacturers don't even spec them as different. Centric and Dorman list the entire range of BBP cars with 10" drums from 65+ under a single part number for the wheel cylinder, they're all 15/16" and 3/8-24. The Dorman # is W78734, Centric is 13563001 for "standard" and 13463001 for "premium", but the date ranges are the same for both, as are the bore's and bolt sizes.

Raybestos, on the other hand, breaks it into two different part #'s, WC37053 for the 65-69 cars with 15/16" wheel cylinder bores and 3/8-24 bolts, and WC37235 for all of the '70+ cars with 10" LBP drums, those are 15/16" with 7/16"-24 bolts.

And actually, the 11" LBP drums used the same 15/16" wheel cylinders, the later Raybestos part number is the same for those too. Or either of the Dorman or Centric #'s.

There are 7/8" wheel cylinders out there too that work on both the 10" and 11" drums, they can be used to alter the front-rear bias a little, for example, if you run 11x2.5" rear drums with the smaller 10.8" disks in the front. Those are WC37236, and they have a 7/8" bore with 3/8"-24 bolts. They came on a few years of some of the trucks and vans. But everything else ran 15/16".