I would guess it's a Dana 60 or a GMC corporate... But I really don't know. There are rumors of a 3.90 gear set for the HO52 rear axle, but if it exists, it would require a 1962? or later carrier. It's possible it is the original axle with a newer pumpkin, but the chances are it's a newer axle with newer brakes and everything.
That won't help with the front brakes, but you may find they've already been swapped to bendix if a big "resto" was done. If not, when they need doing you may find the parts available from folks here.
Good luck and good hunting!

Current fleet (subject to change w/o notice)
\'49 GMC 3/4-Ton , 60 Austin Healey Frog-eye Sprite (some assembly required), 2011 Dodge Avenger, 2015 Jeep Cherokee. No, they don't all run.
My other ride is a (B737)no, (B767)no, A320.... Update... was Embraer E190, now Boeing B787.

Knowledge is a wonderful thing, but ignorance means you don't know you can't do something.