Lots of options out there, a C/K20 14BFF will bolt in directly, a C/K30 rear axle can require some perch movement (though my C30 axle didn't). If you're willing to move perches, you can pull a rear axle from a newer truck as well (do know that after 2011 the lug pattern changes and wheels don't interchange).
As for the D60, I think all the GM D60 axles are equally interchangeable. I think.
Yoke sizes, brake styles (mostly e-brake cable differences), shock locations, and spring widths are just about the only potential snags here. Get the spring/shock perches lined up and you should have an easy swap.
Do some reading around here, lots of folks have run lots of different axle combinations with varying degrees of ease.
