Ok, I know some of you out there know these engines, and I know this question will make me look dumb, but hey, so be it.

I'm tearing down this 6.2, pretty sure it's out of a 91. Anyway, on the block, where the oil pan gasket would sit, there are letters stamped at each cylinder. 7 of them are "C", one is "D". Does anyone know what this means?

Thanks in advance for your help.