I think it is a C96 stock that has been re-fitted with a stock iron for a different pistol. Luger? maybe... some early Luger stock irons had push buttons instead of levers...
I have never seen a DWM cartouche on a stock like the one in this auction... so I can't offer an opinion as to whether or not it is original, or added to give the stock some additional character or inflated value. Certainly doubtful that DWM manufactured Mauser C96 stocks... but not impossible.
But in reality could be any pistol that has a similar shoulder stock lug to the one that is standard on a Luger... Lahti being an example...
