I think I understand, the pin (viewed from the top) sits at about the 11:00 position with the gap of the ring at about 11:02. Therefore, as you say, the gap is hidden from the ports. I noticed also when installing the retainers, the groove on one side was filled with what looked like lapping compound. That would have been a real problem I suspect if the retainer didn't seat. Also, I noticed the new piston had a number '4' cast in the bottom. The old piston had a '2', what does that mean?