[Gary Dillard]

Here's my thought for a simple (possibly) redesign that may work:

The only critical dimensions you need are the diameter where the ring gear mounts, diameter of the pins that hold it in place (looks like 3 places equally spaced) and the distance from the slide rods to the center of the lens / ring gear.

Buy a stock gear (aluminum probably for strength and weight) that's slightly larger than the camera diameter - scale it from the picture. Bore out the hub to the mount diameter and add the pin holes. This will give you a gear on the camera similar to your picture.

Buy a stock gear that's about the same size as the picture or smaller (can't tell what gear reduction is in the housing), same pitch as the ring gear you bought. This gear will mount on a shaft on an "L" bracket that sits above or below the slide rods and meshes with the ring gear - determine the placement on the bracket from a scale drawing with the rods and the lens centerline, or trig it out.

Buy a stock knob of your liking and mount it on a shaft on the L bracket as well (or an adjacent bracket) normal to the gears as shown in the picture.

The purpose of the system is to give precise motion to the camera with coarse motion from the knob; similarly low forces on the knob become high forces on the lens, which I believe is the reason for the pulley so you don't break the lens. The system also changes the rotation 90 degrees. You can accomplish the same 2 things with a flex shaft (like the FIRST seat motors). Attach one end of the flex shaft to the knob and the other end to the gear shaft. For these loads you can probably use set screws (forgive me Woody) to transfer the torque. You may need to restrain the flex shaft somewhere in the middle depending on the load but hopefully not.

Mount the L bracket(s) to the rods with saddle clamps - complexity of that attachment depends on how often you plan to take this on and off.

Good luck.