That is a Rockwell 221, Napa has a bunch of the parts, look on their website, it listed some parts (I saw them just today).
A total rebuild kit should be easy to find. I did a rockwell/dana 221 google search and found a company that sells a kit....don't remember what co it was. The output bearings are ball bearings, a guy said they wear out fast??? I have 3 extra t cases.


64 & 66 GMC long fleetside 4x4
Cartwright, OK