I liberated part of an arm from a dual monitor mount I had lying around. As I had dismounted the DRO I had to manually machine the mount the old fashioned way.
Power supply mounting for the Pi and screen is still up in the air (dangling wall-warts) as it turns out that USB-C power connections are complicated and powering from the chunky 5V supply in the control box is not going to fly.
The backboard is a piece of 16" melamine shelving which give the whole thing enough weight for the support arm adjustment to come into range and the Pi tray is the last part of an old datacenter keyboard tray I've been gradually scavenging from. The monitor is mounted with industrial strength Velcro. 3/4" x 1/8" steel strap and #8/32 screws holds it together.