Waidmannsheil,
Re the Mauser factory mount, i can help a bit here. The pushrod in the bridge most likely has a leg on the bolt handle side of the bridge. The leg engages a shallow recess in the foot on that side.

The recess is within the edges of the foot.

If you have Speeds first book about Oberndorf Sporting Rifles there is a good image on page 265 illustrating the design.

GABE93