that looks like a part number, and is likely to just be "GM" as they use common parts - for the year ID, if a 55+ Chev frame, the main part of the vin will be stamped on the top of the drivers side rail in front or behind where the steering box mounts - the number will start with the 2 digit year designation, like 56L####### - not sure about GMC's location, but the number pattern would prolly be different
Bill
