You know, I tried it on some of my other Lugers and it fits differently on all of them. The only one it fits perfectly on is the 1939 Nazi Mauser. It's sloppy as heck on the 1917 Erfurt shooter...
I was looking at the lug and I think it could stand to have just a hair taken out of the notch. I'm not going to go and grind on it, but that's clearly what it needs.
I took a look at the picture and description from Numrich on that holster. It is supposed to come with a mag pouch and straps, but it has neither. I'm going to call them tomorrow.