You have a Ford rear end so why not use Ford brakes. The 5 on 5 bolt pattern is a Ford bolt pattern and they did use disks on some of the larger Ford and Lincolns. I think you'd be better off just heading to the local wrecking yard and looking for a set of caliper brackets for your Ford 9" and then buying a set of Ford calipers and rotors. You can always have the axles and rotors re-drilled for a GM bolt pattern if you want.
"Speed has never killed anyone, suddenly becoming stationary, that's what gets you." - Jeremy Clarkson