1956 ford part # is AB 7561-a and 1957 ford part # is B7a 7561-b and these are listed as different parts in the classic car catalogs and the appearance is different; mercury is similar but different. The bearings look the same, at least on the fords. The clutch release lever, B7a 7515-a, shows the same from 1952 to 1959 ford Y-blocks.

Are any of these hubs interchangeable? If not, is there a simple explanation as to what is different?

Thank you, Pat in Arizona