Kevin,
A search through the
GM Heritage Center resource documents shows that the "AB" code was used to identify the common passenger vehicle rear axles mounted behind all equipped with automatic transmissions from 1955-1964. "AB" is specified as manufactured at the "Gear & Axle" plant in Detroit, MI.
None of the specific year GM data files noted what the gear ratio was for "AB" designations, but researching other Chevrolet vehicle description documents shows that the "3.55 to 1" was the standard ratio behind automatic transmissions for those years.
The only specific engine package detail I found when searching all those year documents was for the 1959 model year which indicated it would have been installed in "348" equipped vehicles with either of the available automatic transmissions or the 3 speed manual trans option. Otherwise the only note was that it was used behind automatic transmission equipped vehicles (no specific engine).
Somewhere on that case there may be a "cast" date code that may better identify the actual year of manufacture.
Hope this helps???
Dan
