I did a ground-up on the same bike. Mine was registered as a '68 as well. Honda's last one was really a '67, but they got registered when they were sold. Someone added those turn signals and the seat isn't original, but it's very rare to find them with the original pipes still there. Are the pipes solid? Holes?
Also lucky to have all the side covers and an intact front fender. Everyone bobbed the fender when they were kinda out of style.
This place has a lot of reproduction parts, and they're very nice people....
http://www.classichondarestoration.com/honda-cb72-cb77/cat_3.htmlAlso Western Hills Honda in Cincinnati has parts.
Unlike the CB750's there's very little available from Honda. Good Luck! Nice find! John.
Don't hesitate to ask me questions, should they arise. John.