Okay... According to info I have found to update my 49 3/4T: GM used Eaton HO52 and HO72 rear axles between 1947 and 1972. Most had a 4.57 reatio.

The 67-72 3/4T truck and Burb (either with A/T) had a 4.10 ratio. Some actually had a 3.90 ratio, but are equivalent to hen's teeth. The pumpkins swap for ALL those years. Randy's Ring and Pinion sometimes carry a 3.90 R&P, but they will only fit in carriers from (IIRC) 1962-1972.

So Options are, for older 3/4T: Keep the 4.57. Find a 67-72 3/4T w/ auto and swap the pumpkin. Find a 62-72 3/4T pumpkin and swap in either a 4.10 or 3.90 set, and swap pumpkins.

Re Brakes: Prior to 1951, Huck-style brakes are used (not-self adjusting). The drums slip over the wheel studs and are held in place by 2 flat-head screws (only to keep them from falling off when the wheel is removed).
Later models use Bendix-style brakes. These have the hub assembled to the drum, so removing the drum requires removing the hub and all that entails (yes, I prefer the Huck-method)

Simple answer: The 69 pumpkin will fit real nice, but if it was a factory 3-speed, probably has a 4.57 ratio, same as yours.

Good luck

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.