That can be a bit tricky. There were some engineering changes in the 1956 year. The “A” is the identifier for whether you got the before or after-changes version. Sorry, I don’t know which, without the specific parts books. If the “A” is the after version, then there is a pretty fair chance that the 1957 (CD-14) models would be the same. But certainly not guaranteed. If I remember correctly, the throttle gear/shaft assemblies were one of the changes. Stamped brass gears were the early version, while cast ball gears were the improved version. Having said that, the cast ball gear/shafts could be, and often were, used to replace the stamped ones. Furthermore, I’m not positive that the change was made in 1956.
