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If it's the original axle on the '75 F250 it's a closed knuckle w/kingpins, the '76-'77.5 has open knuckles w/ball joints and disc brakes or you can get a HP44 from a '77.5-'79 and swap it in to get disc brakes.
This is where I got my disc brake conversion kit. If you have the HD D44 "big ball" closed knuckle front end
Looks like a nice kit, but $535 is a lot of green to spend for disc brakes when $150-$200 can buy you a 78/79 HP44 w/disc brakes and you get the added benefit of the high pinion to boot.
I'd have to agree to a certain point Montana - it depends on where you live and the availability of a HP D44. Also, the unit that's found may need an entire overhaul which could cost upwards of 1K dollars (new bearings, races, ring/pinion, seals, tie rod ends, drag links, etc...). Then, if you're **** like me, it'd have to be tanked and either painted or powdercoated.