Jay... Thanks for the photos of your (Dave Kings?) installation. That definitely looks like the way to go. As I mentioned I used a RAM 'ball/socket' mount to clamp my old plotter to the Dodger rail. I forgot RAM also made swing arm mounts as well.
It's my lucky day as I was able to pick up a brand new RAM double swing arm mount similar to Dave's (but with the 2nd arm a ball/socket) off eBay for $36.