Ron, I have never seen one like that, and am just wondering how I missed it if it is so common. Also, I don't see the purpose, It looks like it would require a special forging and extra machining to make it with that cutout in the middle and then even more work if the rear boss is as high as it looks, not to mention that a special screw might be required. All in all, not to K.98k specs and something I think would not be done in wartime. I just wonder what the advantage could have been.
I am of course assuming that those bolt stops are original and not something made up by an importer or a parts place as replacements, also a possibility.