Pistons in GMC sixes from the 40s and 50s came with two numbers stamped on the top. 1 thru 6 for the cylinder number they were installed in at the factory and another single digit for the actual piston size. Below is the size chart for 270 and 302 engines.
'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.
