So I am finally getting around to replacing my Top end with my Pro-X pistons and modified cylinders from Bill Bune (that I had received late last year). This is for my 75 RD350. I has 2 rings and a oil expander (assuming this is what the corrugated ring is- does not look like the one in the instructions, stating for 4 stroke only, attempting to upload a pic but phone is temper-mental today)). I did not receive any instructions and found a generic set online. It was very difficult to see the ring profile edge (to determine what was top and what was second ring) so I measured these with a set of calipers and measured the ring lands within the pistons with a feeler gauge and found that the top is thicker (.059") and the 2nd ring is thinner (.046"), each marked with a "T" so I can install correctly. My question is that I do not see where the expander is used, assuming it goes behind the top ring due to width being .056" thickness. can anyone confirm this is where the oil expander goes, behind the top ring or is it not used at all?