The product code was 323 for the CB500, which is what the pipes were originally designed to fit. There continued using the same pipe on the Cb550K through 1976 (US models).
The muffler shells are stamped/formed in a big industrial press. They are a welded together as a unit and then chromed. Not considered rebuild-able.
You'll notice they have a top and bottom "seam". I've never cut one of these apart to see what's inside. They usually have holes through the outside if the internal baffles are still intact.
It wouldn't surprise me if whoever drilled holes in the exhaust for more noise didn't try to eliminate the baffles inside the pipe too. The infantile seem to like making big noises. If you can't make it go fast, then make it louder. But, I digress.
I've got an extra #1 muffler with a screwed up head pipe. And, I've been toying with cutting the muffler apart just cause I like to know what's inside. The issue is, of course, "spare time".
Cheers,
P.S. I drove for years with a 4 into 2 system 'cause I thought the stock pipes were too expensive. The 4/2 worked ok. I eventually sprung for the stockers despite the expense. They aren't that expensive really, if you amortize the cost over the life of the machine, and take into account that you purchased the bike cheaper because of the worn out exhaust. Sure makes tuning the bike a lot easier, too. To me, that's worth something. Besides that, some willingly pay more for "style points". With all that factored, I think they are worth it. IMO
