Just picked up some Muncie parts, case extensions and cases. One is a "660" case wiht teh following markings:
P9M23 which I decoded as Muncie, model year '69, assembly date December 23.
42311 which I decode as Chevy Transmission (replacement part) model year '68, sequence numebr 42311.
any clue why the replacement code indicates for model year '68 and the assembly code indicates for model eyar '69?