Joe there are kits around that use Calipers from '76-78 Cadillac Eldorado and Lincoln 11" roters. If you do a search on EBay for "Rear Disc Brakes" you should get some returns. There are pictures of brackets you could use as a starting point plus other items for sale including refurbished calipers. The neat thing about those calipers is they have a parking brake set up.

Let us know how it works out

Pat