Your truck would have been stock with Huck brakes and a lot of guys prefer the later Bendix type. You have to change so much to convert the early axle to Bendix that you'd probably be better off swapping axles.
That same basic axle design was used into the early 70's so a stock type axle is not hard to come by. I have two of them setting in my yard right now...
I recently put a GM 14-bolt under the rear of my '54 GMC 1-ton. Though mine is drum brakes, the axle is available with disks. Since you are not trying to maintain hauling capacity I'd suggest starting by figuring out how you are going to convert the front to disks and then limiting your rear axle search to those with the same bolt pattern.
There are no disk kits available for a 3/4-ton. You are either making up your own conversion, copying someone else's, and there are a few documented on the web, or swapping to a 1/2-ton front axle and using the 1/2-ton conversion kits.
The 1/2-ton conversions are either 5x4.75 (Chevy car) or the same six-lug pattern the stock 1/2-ton uses.
