A Dana 60 from a 3/4 ton Ford will work fine. I got mine out of a 76 F250. It have 4.10 gears and a trac-lock, that I ditched for a new powerlock with 35 spline gears. Obviously, you'll neeb new axles housing ends, brakes, axles, etc. It was still quite a bit cheaper doing it that way than going with an 8-3/4 starting from scratch.
Here's a great tool for calculating tube length, etc so you end up with the pinion in the stock A-body location, if that's what you're looking to do:
DoctorDiff Axle Calculator
