5th picture down at the 2 o'clock position it kind of looks like there's a couple of chunks missing from the piston crown?
Those are original from the manufacturer. They are for piston orientation. Probably face the front of the block.
Old school performance adder - if you reuse those pistons, turn them around so they face the back of the block, less friction due to the pin not being in the center of the piston, but you might get a little piston slap noise.
