Joe,
I was just reading some stuff on that buttonholer, and you may be able to use it on a 66-1.
At the time yours was made, Famous had a C for non side clamp machines and a CC for Singer type side clamp machines. there was also an F style for Free made Rotary machines of that vintage.
I read that the 50th Anniversary was from around 1940, but I don't know how accurate that is.