Have not heard of that before.
When you turn the screw does cam and shaft also turn? If no screw is stripped.
If yes - is the distributor all the way down/seated on the head? Then it is possible top port of the shaft is not sitting down far enough to key into the bottom part of the dist. shaft.
It is also possible that this part which is pined and fits on the distributer, and fits into the head hole has a missing or broken pin.
https://modelastore.com/electrical/distributor-distributor?product_id=4223
When the cam and the shaft rotates in a good motor, the entire motor works - points cam, dist. shaft, valve cam, timing gear, crank gear, crank, rods, pistons. All is mechanically connected.
Assuming the cam screw turns easily and is not stripped, would not think it would be inside the motor, so hopefully it is one of the above.
To get it out and the points cam is turning, you will probably have to use a vice grips or lock jaw pliers on the cam to hold it still. If you do this you will most likely have to replace the cam, and the washer between on the cam screw and the cam. Issue doing this is soon as the cam screw starts loosening the cam moves independently on the dist shaft. Timing on an A is not performed by rotating the dist like on more modern cars, but by positioning the dist cam properly and tightening cam screw.
I you can't get the screw out, hopefully the methods in the post string work.