You can thank my old landlord for not having an axle to give you-
An axle from a 78-79 F250 is ideal, but one from a 75+ F250 works, as long as you get a high pinion axle. You do need to make new perches and get new springs, the rear springs are the expensive ones, though. I went with Explorer Pro-Comp springs, and was able to get rid of the rear blocks so I didn't have any axle wrap issues. They were something like $350 or $400 for the pair, but well worth it.
I do have the steering linkage to throw a straight axle under your truck I'd be happy to give you, though.