after they quit using engine numbers, GM called them
VSN's, Vehicle Serial Number - around here we usually refer to them as "vin"s lower case to differentiate from "VIN"s, uppercase, standardized by the feds in the 80's - when you get a title the VSN will be entered under the box labeled VIN, so when talking to the DMV, it's a VIN or vin, even for the years when the engine number was used on the title
Bill
