Rob English (who I think qualifies as a GMC guru) posted this GMC serial number decoder over on the OldGMCtrucks web site that has a bit more detail.

GMC truck model identification.



This page shows that GMC did use frame stamped serial numbers on earlier trucks.

Serial number locations


Source is:
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Last edited by Bill Hanlon; 04/26/2022 12:25 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.