11 3/4 brakes

I did this swap to my 64 sport fury. Used late B body caliper brackets with the 76 f body style calipers and a 74 A body prop valve. I had to go from a 15/16 bore mc with the old 10.87 rotor and smaller 74 A bodycaliper to a 1 1/32 bore mc with the larger calipers. I have 11 inch rear brakes from a 69 RR. So far I'm not impressed with the braking. seems the same as with the smaller rotor/caliper. Any thoughts? Sorry for hijacking but the answer may help others.