I would like to throw my solution into the hat.
I like to keep things simple and use proven techniques.
I worked on a large A4 Gear some years ago for DCU Models. I pulled out an old prof of concept prototype from storage and made some updates to it last week. As you can see its is a simple torque rod arrangement that allows the rod to slide so the shrink link can do its thing. I just tested this for stiffness and it is very positive even with the nylon arm I used. Any production set would have all aluminum components to make it even stiffer.

The good news is this will work just fine the bad news is, the Comp Art retract is not a compatible configuration for the torque rod.

I would need to look at the Comp Arf gear to be able to see if it could be saved or changed in some way. Just PM me if anyone is interested in working on this with Matrix.

Thanks,