Never saw anything about shortened serial numbers but did see something about not having a VIN # means it may have not been produced for use on assembly line to go into a car with a VIN # to match. I have included a better picture of the serial #.
!956 was the last year Chevrolet put serial numbers on their engines. From 1957 on the engines just got an "engine code"...Plant, Month, Day and Designation. So all of the regular production 283's coupled to Powerglides built in Flint on December 5th got the same code you have and they headed straight to the assembly line. I'm not aware of any regular production Chevrolet cars or trucks ever having the engine serial numbers match the body serial numbers.
Mike B
