I believe that the consensus is that your spinner was a failure by the quality control department. I checked my Proto spinners and all of mine were assembled with the 1/4” female drive in the conventional position.
-Don

My postwar Plomb spinner with a similar handle shape as your early Proto spinner also has an operational 1/4” drive female socket as expected.




I have more than a few Plomb spinners and none of them have a socket similar to yours.
