Short and sweet-
you need oil ring spacers with this design piston, not that moving the oil rings up and down in the groove wouldn't have given a clue. Oh, and you don't put orange silicone on the rear main parting halves to make sure the oil passage seals. It tends to plug the hole when you torque it down.
Making sure that the rocker slots clear the studs helps too, but I knew that was not checked when I installed the roller rockers.