Great info on this thread. I swapped an entire suspension from a 2006 F550 onto my 2001 F450. I had a shop do most of the hard swap stuff like rebuilding and regearing axles, steering etc. One thing I ran into when researching the swap was the nomenclature. You see the terms "Dana 60", "Super 60" and "Wide Track Dana 60" and the like thrown around willy nilly. Understand that if you are doing the swap, make sure you get a set of Wide Track Dana 60s from the 2005-on F450 or F550. If you are going through all of this trouble, you want the tougher axle with the wide turning radius. I bought not one but 2 donor trucks. One at auction, one on KSL. First one was listed as a non-running truck but it had a bad injector. I did a little work and sold it and it helped ease the hit on the pocketbook. Best part of a non running truck is you can get both heavy duty axles with matching gears and all the hangers, mounts, bits and pieces to go along with it. Then sell your existing axles to recoup some cost. Should be able to find a non runner for a few thousand max.
Depending on what you want to do with your tires (minimal lift, dual steering stabilizer, track bar drop, Buckstop Super singles, MPT81 meats etc) you might want to re-gear front and back together, add lockers and upgrade your steering setup. I may go to hydro assist but in the meantime I installed a custom Saginaw steering pump setup with remote reservoir from Lee power steering. Night and day from the wimpy Taurus steering pump they put on these monsters. If you don't want to get that aggressive, you could skip the HD rear and do a normal single setup and match the gears. Sourcing parts in this environment will be hard. Full donor will help if you can find one.
I decided against reinforcing the frame as pointed out above. Time will tell. My rig will be heavy with a camper and I have huge tires but I'm not wheeling this beast.