1. The drive/driven gears are a matched set - matched to RPM-affecting features of the truck (rear-end-ratio and rear-tire diameter).
2. However, (I think) some sets of drive/driven gears might contain one gear that is shared with another set.
I dimly recall someone posting a gear-set parts list that showed part numbers for different combinations (I will try a search, but the info might have been posted in another discussion board).
I think the drive can be carefully punched/pressed off the forward yoke for the u-joint (I have only done it once - for my 1954 Suburban).
added later - not the charts I referred-to above: Master Parts Catalog: Group 4.337 (and more parts in 3.338)
