All single rear wheel superduties from 99 to 01 came with a dana-50. Only the duallies had the dana-60 those years. In 2002, ford put dana-60's in everything.
On the superduties, you've got metric 8x170 bolt pattern, unit bearing hubs (super spendy on the fords, 300-ish per side), and vacuum operated hubs, but they are disc brake (anti-lock on 2000 and newer).
Early 99 trucks had smaller sector shafts, and smaller track arm bolt hole, hence almost no lift kits for early 99 trucks (built before 3/99 on door sticker).
Superduty VANS on the other hand, to this day still use the older 8x6.5 standard bolt pattern wheels!!
Unit bearing hubs on superduty axles suck once you put a big tire with tons of wheel offset. DYNATRAC sells a conversion kit that turns the dana-50 outters into dana-60 outters, gives you a fixed spindle and manual warn hubs. They also sell a crossover steering kit that replaces the outter knuckles. Awesome kit, but its 3000 bucks for everything.
That said, I dont personally know anyone that has destroyed a superduty front axle. Dana 50 or dana-60, and we drag race and sled pull the crap out of them. 4-wheel drive, 20lb boosted launches on pavement with 35" tires and 8000lbs of total truck weight.
Lets just say you wont be seeing any 1 ton chevy IFS trucks doing that more than a couple times. I have about 7 race seasons of doing that to my truck.