That 52 5/8 is for 1 7/8 brakes. The big bolt pattern axles sticks out more and uses 2 1/2 brakes.
The dana housing I'm building now for my duster will be about 51 1/2 housing flange to flange.
Since the Dana was never used in any A-body except the 68 SS cars there really isn't a spec to go by so if your cutting a housing down you can cut it the length it takes to end up with 52-5/8" drum to drum. Same for an 8-3/4
