NOT 52 !!

Arrr.... it's my pet peeve.
Never measure the inside of the backing plates as an indicator of total width. That assumes whatever you compare with has the same brakes, and 50's brakes are shallower than 60's ones. It's like measuring to the inside of piston skirts and saying your 428 has a 3.84" bore.

A 57 housing is wider than that and for comparing you have to remember that a Granada 9" or the 66 Mustang 9" is the same overall width but the axles stick farther out of the housing than the 57 so the later housing itself is narrower.

The only measurement that matters is to the outsides where the wheels bolt and the pinion offset. An early bronco is also that width but the pinion offset would put the driveshaft into the right side of the tranny tunnel.