Using mustang rotors for 4.5" bc

See that's what I'm trying to figure out. So you're saying you couldn't just pick up a set of their 4.5" rotors and slap them on the cars that already have KH calipers? Mine has the whole kit since mine didn't come with the KH calipers but I assumed you could just buy their rotors and slap them on if you did already have them.