[Mike C]

If it's the Dana 60 which the military truck should have had then you will need to buy hubs for a 60 and not the Dana 44 hugs. I think your original hubs are the external ones on the K20 and are not compatible with later stuff. But maybe?

If memory serves thought, the 77 model year was the first for the K30 though, but that's what all the Military trucks were I thought?

But 60's bring big bucks so maybe something else was swapped in to sell the truck again?

Cliff Notes version: Early K20 hubs different than later K20 hubs which are same as K10 hubs. K10 hubs interchangeable all years, Dana 60 gets it own hub.