The issue is whether your Rally II's are 14 inch (OEM) or 15 inch (2nd Gen or GTO's).
Most disk brake kits will not work with 14 inch Rally II wheels. However, there are some models of 14 inch Rally's that were designed for the original (crappy) 4 piston front disks. That info is on this site someplace.
So, the bottom line is that a disk brake upgrade with your existing Rally II's is a crapshoot with 14 inch wheels and absolutely no problems with 15 inch wheels.
Others have found that they can get by with 14 inch wheels after a little bit of grinding of their brake calipers.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
