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You don't need the radius arms, just spindles out. You will have to change out the steering linkage if memory serves as I think the tie rod ends are larger on the disc brake spindles. Don't quote me on that- I changed mine over to the later style steering gear at the same time, so I had to either way. Brake hose mounting took me a bit of modification as the older axles do not have the same mounting points. You will have to change out the proportioning valve and master cylinder to disc brake style as well. As ND already said, 76 up will work. If you change the steering linkage, you will have to go to the 78-79 T-style because last I heard, one of the tie rods is not available for the 76-77.
He's got a 4wd though he said. Are the calipers the same? The rotors, hubs (if separate like the 4wd is) and knuckle/spindle would I thought have been completely different?
Never played with the 2wd brakes myself, so I'm only quoting what I think are the normal differences. I actually did use 2wd brake hoses when converting my '71 Bronco D44 to Ford discs. The '76 and '77 EB hoses used a larger thread at the axle end, but the 2wd pickup hose fit both the caliper and the original steel lines on the Bronco.
oh, and if you don't find someone here with the stuff, Randy at Driven Auto Parts is a Ford (mostly Early Broncos, but probably much other stuff as well) in Phoenix is a great source for used Ford truck parts.