seller probably has been talking with the man from planet Mars....... ? Flat out f'n nuts is about all i have to say.
did later production "K0" bikes come with HM300's from the factory ? if they did, they would have been the same HM300 units as the early K1's. i seem to remember the early HM300's had no relief on the #3 pipe and other subtle differences from the later HM'300's.
Albeit, oem, being these HM's are post-1971 replacement exhaust of the "paragraph" type, they won't be correct for any "K0" and K1 that came out of the factory during that era.
the bar code was first seen on packages of Wrigley's chewing gum in 1974. i doubt Honda was using the bar code in 1974. for some reason i seem to think Honda didn't come out with paragraph HM300's until the early 80's. i seem to remember there is a date within the paragraph.....
Who knows or has a picture of the paragraph verbiage ?