Can someone tell me the correct backing plate numbers for the 2 1/2 inch rear brakes? I have looked a 3 67 Shelby`s now and found K+H 71086 and 70858 on them all. But I`m being told that there are also bendix numbers 21882-L and 21993-R? What years had which? Also being told that my 69 GT500 should have them? And not by anyone I would consider an expert. Is this true? Anyone know what came on what?