My Rodie is an old XR-Heligon 50mm f/.75 with a K5 + K2 glued onto the back. It is too heavy for any helicoid to support, so I just move cam and lens until I get something interesting. I don't know what causes mine to create "wheelies", but it gives me joy.
I also have an XR-Heligon 68mm with no f marking. I've not yet added a K2 to it.