20 years ago when I swapped out my 14-bolt's drums for discs I used the rotors, backing plates, and calipers from the front of a 3/4-ton. Back then there was no Internet, and custom 4x4 fabricators were very local.
I had to drill/modify the backing plates, and have a machine shop build me a couple of spacers.
Things are much easier now with all of the laser cut parts available out there. But the two disc brake conversions I did back in the early 90s are still stopping the trucks I put them on.