I recently corresponded with someone over on DoTheTon about a set of these wheels that have been in his family since new.
Apparently, the caliper holder and master cylinder bracket were part of a kit. Or else, it's pure coincidence that we both have the same home-made brackets.
Here are a few tidbits that I cut & pasted from our conversation about the wheels:
"I corresponded quite a bit with other 650 owners about the wheels and found out a few details. The Shelby-Dowd versions were made for both Honda 750 and Yamaha 650. The Yamaha wheels were apparently an Yamaha accessory item patterned after the Shelby wheels and would also work on the RD 250/350. "
"Some of them were made by Shelby-Dowd and I think Yamaha had some made. Most of the time they are referred to as "star" mags. They were sold as an accessory item for Yamahas and Hondas, although I've only seen one set on a Honda. I have a set of the Shelby wheels. Both sets are pretty rare."
I never knew they also made them for the Honda. The Shelby Dowd wheels for Honda are similar, but with more spokes in a tighter pattern. I've never seen a set of Star/Pentagram wheels for a Honda, myself.