..... it maybe me, but they look a bit strange.
Here's old style cylinder from my car. It has dome
here's set of new style cylinders - they have groove for ring, somebody posted here:
http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/488270-1992-porsche-964-piston-set.html
Yours look like someone machined recess... also recess surface does not look right, it should be mirror flat
Part number is for newer style.
Unless it's photo that makes it look weird
