If the post may turn (pivot), should the hinge assembly be mounted on the other side of the post to represent the left shoulder socket?
No, Sketch 1-L should remain as it is.
As stated in its caption, the drawing is meant to depict the Geometry and Physics of the Uncompensated Golf Stroke, not how it should look or feel. And the Hinge Assembly's Action and Function remain the same irrespective of its location on the Post.
It is true that the Golfer's Hinge Assembly is mounted in the Left Shoulder (7-10), and in my early TGM years, I was puzzled: "Why," I asked Homer, "is the Hinge Assembly in the drawing located on the right side of the Post instead of the Left?" His response?