Mearly a suggestion... but it comes from personal experiance. Even though the aftermarket for early SOHC CB750's parts is over run with vendors, the 79-83 DOHC CB750 custom parts suppliers are scarce.
Cycle-X has some stuff although very limited... and Benji's shit is WAY overpriced with reportedly shoddy workmanship and customer service. Other than those two it seems it is an open market for the taking. And those bikes were the staple of the Honda line-up in those years, turning out tens (if not hundreds) of thousands of C, K, and F models. They seem to be rapidly gaining popularity in our circles.
I may be a bit bias, but knowing other owners here have the same concern. I belive custom seats, knee-dent or CR style tanks, upper triples, and side covers would sell like hot-cakes.
Pick up a DOHC frame and start bangin out some parts that fit. Just a thought.