You might not find drums for your original rear, but what else can't you find?
I've found everything I need, and many others have rebuilt and still run the original Eaton. Even the 4.10 gears aren't that hard to find used.

I do like the 14 bolt, but it's not a necessary swap.
Have you looked for disc brake brackets for the old Eaton? Pretty sure they exist in the 4x4 aftermarket.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-