I just looked it up on the Nighthawk forum, while exhaust port angle and spacing are the same or close enough between the 91-08 CB750 and the 84-86? CB700SC & CB750SC, the spacing on the DOHC CB650SC is different. Elsewhere in the world the DOHC CB650SC was called the CBX650 maybe that will help you to find something.
If you're out of options you can always chop and cut and weld until it fits the way you want it to.
Honestly I'd do a few and keep the best for myself, the others can go on eBay or sell on a forum to other DOHC CB650SC or CBX650 owners, that way the whole venture is zero cost.
EDIT: specified DOHC CB650 models.