I have among my hundreds of '54 Merc spare parts a NOS blower/fan switch, part # B3AZ-18578-A.  The part number indicating fitment for a 1954 is FDC 18578 B and I am wondering if any of you Y-Blockers can decode the prefix (B3AZ) as to year specific for this switch.  It is possible that it fits '49 - '53 which obviously would not be in the Y-Block era, but some of us straddle the line with the flatties.

Any help out there?