Having two and hating the grip safety I altered one internally to eliminate it, of course on the outside the grip safety is gone too. Then I had my GS provide walnut to fill in the slot where the grip safety went between the LH grip and the frame, and after gluing it in he checkered it.
The other one is unfired in the box.
BTW, other than the stupid little brass pin that's supposed to align the grips I can't feel the difference between my 1920 Commercial P-08 and the Interarms guns, but maybe I'm insensitive that way. That pin allows the grip panels to move around slightly.
The fit of the grips to the frame though is not as good, there being a bit of grip overhang past the frame on both sides. Not noticeable to most people I think.
In spite of my complaints I love both of them as well as the 1920 DWM. The Interarms Luger is not a true copy of any P-08 model in very small ways.