I heard that the disc brakes from an early 70's Maverick or Comets will work with some mods for a mounting of the calipers. I thought I read it here or maybe ona site called Ford Econolines. They said the bearings from them are the same as the single axle I beam spindles.
I would check that avenue out. Be a cheaper way to go with very little modifications. I know guy say the Maverick disc brakes will fit some 60's Mustangs.
But I will admitt I'm not a 100% sure here. I just seem to recall reading about this many years ago. I could be mistaken. But it is an route to look at.