Hofner 1960s acoustic guitar: Weird neck, what do?

My Hofner from 1960s ish west germany (serial 201946) has a weird neck and Im not sure how to adjust my action.

When I got the guitar it had a shim glued under the fret board that has since come undone. At first the neck would pivot like it was on a rod perpendicular to it inside the body of the guitar. As we were just about to glue a new shim down the whole neck slid out on accident (after trying to make it do that for hours) that's when we found all its quirks out. Theres a metal hook that clamps down to the inside of a metal plate inside the neck. You tight and loosen this clamp with a hidden screw that seemed like an old button hole that was hidden by a bit of metal right behind the neck.

Now the neck pivots drastically less with the screw being tightened but it still pivots enough to be a problem. Is there something Im missing, or another hidden screw or something?

I dont think glueing another shim in place is the answer and would like a professional's opinion on what to do in order to make the neck stop rocking and maintain my action.

-Also, yes, the screw is tightened as much as it can be with hand torque

tl;dr: Neck pivots on a hidden hinge inside of the base of the neck. Is there a Proper way to make it stop rocking without the use of glue?

Thanks PS - Photos to come