If you look carefully at the piston tops (and if they are original pistons) you will find two numbers stamped. One is the cylinder number, 1 through 6, front to back of the engine. That is so you can put them back in the proper hole if you remove them.
The second number on the piston should have a matching number on the top surface of the block. I can't find the decode table for a 228 right now, but the attached table for 270/302 engines works the same way.
After the block was bored at the factory, the cylinder was measured and special factory-only pistons were fitted into each cylinder. The piston had a number already stamped on it signifying its "size". The piston was installed into the block and the corresponding number was stamped in the top surface of the block.
Pistons with the number 1 stamped would be fitted to 0.00075" to 0.00100" under sized cylinders. Pistons with the number 2 stamped would be fitted to 0.00050" to 0.00075" under sized cylinders. Pistons with the number 3 stamped would be fitted to 0.00025" to 0.00050" under sized cylinders. Pistons with the number 4 stamped would be fitted to standard size to 0.00025" under sized cylinders. Pistons with the number 5 stamped would be fitted to standard size to 0.00025" over sized cylinders. Pistons with the number 6 stamped would be fitted to 0.00025" to 0.00050" over sized cylinders. Pistons with the number 7 stamped would be fitted to 0.00050" to 0.00075" over sized cylinders. Pistons with the number 8 stamped would be fitted to 0.00075" to 0.00100" over sized cylinders.
'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.
