Here is a composite shot of the interior of one of the pistons. The stamp "1275" probably indicates that it was cast in December 1975. The other marks are the Kolben-Schmidt logo, what looks like a 19 with a 7 underneath it turned sideways, the number "094022" which is probably the mold number, and a "2" and a "7+" underneath the mold number. Not sure what these last two numbers might mean. Maybe the "7+" has something to do with the weight or weight group.