Acutally, if you have Mustang II spindles, there are forged brackets available to mount 10.5" GM rotors (4.75 bolt pattern) and mid 80's GM calipers to those spindles. Stainless Steel Brakes Corp and Progressive Automotive have these. Probably a few other companys as well.
P.S. I've heard of a few problems with the flame cut steel brackets not fitting and bending.
