Eli's comments & questions have got me on a roll.
I contacted the Ebay "K0" seller. The pipes have "HM300" stamped in them, with NO relief or "indent."
Seems like i heard somewhere, at some time, from someone of "stamped" HM300 pipes WITHOUT relief.
Does this mean there may actually be 4 different types of exhaust?
1. "Plain" or unstamped exhaust with NO relief.
2. "Stamped" HM300 exhaust with NO relief.
3. "Stamped" HM300 exhaust WITH relief (original issue)
4. "Stamped" HM300 exhaust with relief made at a later production runs?
My 4363 has the exhaust mentioned in "4" above. They also have some jibberish i cannot recite, that is stamped on the inside of the exhasut toward the rear of the muffler, about not meeting EPA standards after 1983
Per above the "#3" exhaust don't have the EPA jibberish.
Per above, the "#1" pipe, we all revere, cherish & love.
But, the "#2" pipe - seems to be a bit of a conundrum - perhaps ? Maybe this is a Honda replacement pipe of a slightly later production run, prededed only by the "#1" pipe ?
Hmmm........ Great contorversy !