?? Numbers stamped on pan rail of 263 ??

[ebbsspeed]

Along the oil pan rail on the 263 I just started to disassemble, there are several single digit numbers, each seems to be lined up with a connecting rod journal. The numbers are 6, 5, 4, 8, 7, 7, 5, and 6. Also, stamped in the rail next to the center main journal is the number "3", inside of a circle. What do these numbers mean? Thanks!

[Janderson]

I have seen this before on almost ANY make of engine. I am not 100% positive on this (and I am sure I will be corrected if I am incorrect) but to the best of my knowledge it has to do with bore/piston size.

No two pistons are the same size even thought they are machined to standard (or .030 or .060 oversize etc.). So in the Buick factory they would measure each new piston and each one might vary in size by a few tenths of a thousandth or so. Same with the finish size on the bores. So getting the right piston/bore clearance was achieved by fitting the right piston to the right bore. The pistons could have been coded "5,6,7,8," etc. depending on there size. I believe the number "code" stamped on the pan rail on the engine block was to tell the engine assembler what piston to put in what bore.
Just my idea

We always measure new pistons, note the differences, number them, and then size the bores to the appropriate size.