more than likely thos brackets are intended for use with a 1/2 ton rotor for a 5 lug conversion, they need to be offset to work with GM 3/4 ton 8 lug rotors,also the spacing on where the caliper bolts on may be wrong...those look exactly like the ones i have on my rig,i had to weld and re-drill the caliper holes and offset them by 3/8 to get them to work with 3/4 ton 8 lug rotors...pics in the dana 60 folder in my webshots