Looks to me like someone took a grinder to the engine serial number. I can almost read the last digit as a 2. Mine is a lot smoother than yours.

So L198 would be December 19, 1948 and J256 would be October 25, 1946. Check the frame on the passenger's side near the front axle. It may be stamped with the truck's serial number. More stuff about parts and truck ID can be found here.

My GMC Master Parts Book X-154001 covers 1939 thru 1954 GMC truck models 100 thru 470 (all but the biggest trucks). It shows pistons with a compression ratio of 6.75:1 prior to 1953. My '52 has domed pistons with a casting number 2136477 head. There were other pre-1953 head casting numbers used on 228 engines.

In '53 GMC switched to flat pistons with a compression ratio of 8:1.

If you would settle for a .PDF file of a 1953 GMC Master Parts Book, fellow 'Bolter SlimSix (aka Andy) used to sell copies that he had made. Try contacting him via a "Private Message".

Last edited by Phak1; 07/23/2025 12:54 PM. Reason: Typo
'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.