I am not sure about casting numbers, I think there are several different numbers out there, the car's build date was Dec. 1, 1969, the engine build date was 11-11-69, the left caliper is original, and yes, has been blasted, I asked RAMMAN about the numbers on those calipers and I cannot remember what he told me but pretty sure there are no date codes on the calipers but I am by no means an expert on the subject