Well, guess I learn something new every day. LOL I knew the 19's and 23's used the same relatively unchanged action over the years, just didn't know they updated the magazine system somewhere along the way.

Aside from the hole in the side of it, I still say that last photo looks EXACTLY like a current 5-round magazine for a Mark II other than the ears for the retention on the back side are a little deeper on the new ones. If they don't fold around to create a channel on yours, you could try one of the newer ones after doing a little grinding.