There were/are some wiggly exhausts out there. See my avatar for the "Triple AAA" equal length exhaust available in 1970 to 1974. Haven't seen another since.
I have the header in question for my new project, it appears. It is a Laser/Marshall Deep Tone, and if I'm correct it is no longer available for SOHC 750s. I think I got one of the last ones available from a US importer. Mine for the CB750 looks alittle different than the one you've pictured for the 500/550.
OCICBW
PS: Pictures of the Marshall Deep Tone in the first several pages of my build thread.