Well.........what I am learning, is that the stocks and frames varied widely on the 311s.
There were various sized frames, a "square frame" version and a "notched frame" version. There are also variations in tang length. Mine happens to be a notched frame.
It looks like I'm goin' to have to whittle a new stock, which I can do, but really don't have the time these dayz. I guess this one will have to go in the back of the safe until I retire someday.