Is it possible that my 1953 GMC 228 has original pistons? The block number matches my registration.

I had to pull the head due to a possible head gasket leak but now I think it a cracked head at #3 exhaust port. With the head removed I see marking on the pistons and block deck that I dont understand. Each piston is numbered 1 through 6 in order, that part is easy. When standing on the drivers side of the vehicle, the left side of the piston has a "6" and slightly higher to the right is a "9", each of the pistons have the exact same "6"&"9".

The next numbers are hard to describe how they are arranged. On the block deck next to each cylinder is a 5 5 5 6 4 5 and there is a stamp in each piston with the matching number.

I dont think a engine rebuilder would go through this much trouble stamping pistons and the block deck.

Any thoughts?

Pletch
65 Chevy fleetside
69 Datsun Roadster (sold)
68 Chevy long bed step side (sold)
53 GMC 3100 (sold)