Sounds like you have a DOHC mate.
I'm not a 750 man but I'm sure the SOHC bikes ended in '78 (with the "K8"). After that, Honda launched the CB750KZ and the CB900FZ.
As this site is for the single cam variants, you will not find much here - however, there are owners here who own both types and no-doubt they will point you in the right direction (or answer your questions directly).
Cheers