later model frame.. You will have to move the rear spring hangers as the wheelbase is a little different..
There are several posts over on the sweptline forum that will help you. Click on the "forum" and then go to the "Technical" section, which specifically addresses the disc brake swap. Go there, you will find your answer. I've been over there for several years. Lots of knowledge and experience. You seem ready to dismiss it out of hand from your "any more ideas?" reply. The factory power steering is actually power assisted steering. It is difficult to come by, and expensive when you do find a set-up for sale. I've owned several Sweptline trucks with this system. It is a good unit. Find one, rehab it, and take care of it. Far as the disc brakes go, Scarebird has a kit you can order that will take care of the disc brake swap.
Not real sure but I used a dodge d-100 manual steering box on my 1956 f100. I would think that the common f100 to toyota 1979-1985 toyota power steering swap would work on the d100