[66-PMD-GMC]

I have seen a couple of posts on this and wasn't really interested in resurrecting any old threads.
Here's the deal.
I'm mainly interested in GMC trucks over the Chevys so when I have a chance to buy a GMC parts truck or driver I usually jump on it.
I've been trying to find information on the 1/2 ton 6 lug Dana 60's that come in the GMC trucks, 63-66... the BOM numbers are different from the mainstream Dana 60's. ..
I read on a thread that they are assumed to be rare..
I've bought a couple dozen GMC trucks in the past 6 years and 1 out of 3 have had the 60.. the others are 44's so they arent that rare.. I have 9 of them.
The earliest information I have found is for 1974 dana 60's.
Does anyone know of any kind of information on the 63-66 GMC dana 60 6 lug diffs? I need to find bearing and seal parts and no shops in my area have anything for these trucks.