[vectorit]

I am no expert on axles, but there are differences on the axle diameter and spline count on various years/models of trucks that they came out of.

If I was in your shoes, and I had a line on a complete D44 for a hundred bones I'd snag it.
Then take it to a expert and have it gone through.
Ask the expert about your current axle, and inquire about re using the ring and pinion. They should tell you whether or not if it is interchangeable, and check to see of the 40 year old parts are still good.

If it were me, I'd spring for a complete overhaul with new matching gear ratio ring and pinion. I'd also price out a new locker, just in case they had a deal to offer me or if I could afford a new one in the first place.