RBS56: I assume your friend thinks this is a 270 because the engine serial number stamped on the machined flat spot just to the rear of where the distributor mounts starts with "270". If it does, check the other side of the engine block for a 7 digit casting number and a 3 or 4 character casting date. The date will be in the form O M D Y O or O M DD Y O where M is month (A = January, B = February, etc), D or DD is day of the month and Y is the last digit of the year. The O actually looks like the head of a slotted screw.
Some GMC heads had similar casting numbers and dates on the flat top surface between the carb and the valve cover. All this info is useful in determining the birthdate of the engine.
Last edited by Bill Hanlon; 05/24/2026 4:17 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.
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