x2 A 78 or 79 5 lug coil sprung axle will be your best bet. Make sure you get the radius arms, and the brackets if possible. You should be able to get away with your stock spring buckets. You'll have to fab a tracbar mount, Your TTB springs are going to be a little stiff, so I would suggest a 4 inch lift spring for the truck the axle came from. After doing the leaf swap into my F150, Coils seem soooo easy to do.
On a side note, I have a 79 HD Dana 44 in my F150 in my sig. the HD dana 44 8 bolt axles from the late 70's F250's are a little more beefy then the regular 5 bolt. The HD has 1/2 inch thick axle tubes, which is slightly thicker then the dana 60's, although the 60 uses larger diameter. The outers (hubs spindles etc...) can be swapped between the half ton and the HD.