That's true Dwight, the first thing I did after I bought my shiney new F0 was take the OEM pipe off and replace it with a black RC pipe. ($129 back then) That black pipe had much better ground clearance, (the F pipe would grab the ground in bends and threw me and my passenger off before I binned it) had a much nicer "note", and unleashed a few more horses.
The 341's were a disappointment after the 300's, they might have looked the same, but they sure didn't breathe like the 300's. It was surprising how much more power could be obtained just from doing a pipe and jet change, and the other problem with the OEM pipes was that they rusted out very early in the bikes life, and even then, were ridiculously expensive, and most guys wouldn't have wasted the money back then, knowing that they didn't last.
Nowadays of course we don't need to soup up our CB750's because there are so many later model bikes available (that usually cost less to buy used than a CB750) that are so much faster, handle better, stop better etc, so it's nice to put or CB750's back to original condition.
Just like all those years ago, HM341's are expensive to buy, which is why a lot of guys have to settle for an aftermarket pipe, which is probably a performance improvement, (not all aftermarket pipes improve performance, I've got a 4 into 2 pipe here which must have restrictors welded in, it's horrible) but of course, not original.
I recently scored a really nice set of HM341's from another member in Oz, and I'll use them on my K2 resto. They certainly won't be a performance improvement, but they do look nice, especially from the back of the bike, that view is what got me all excited about CB750's 40 years ago! Cheers, Terry.