he cylinder walls on an engine im building are fine but the pistons have divots from what looks to be a couple small screws getting sucked in :/ trying to find out what size the pistons are to replace them. on the inside of the piston is a underlined 6 in a circle followed by gm. on the other 6271096... if that wouldnt be a shortcut do i just take a micrometer to the piston head? if so whats standered. info apreciated.

 

Most likely those are stock-bore pistons. You need to measure the cylinder bores, not the piston itself. The cylinders started off at 4.000".

Since oversizes are typically in the .020", .030", .040", etc., something close to 4", or 4.02", or 4.03", etc., should tell you what you need.