The ramp shown in your photo appears to be one made by the Williams Gun Sight Company. As far as I know, Oberndorf Mauser ramps were either integral, sweated on, or attached with a sleeve, like this one:

You are right. The front sight hood in the photo is not the correct one for a Williams ramp. They are available from Midway: http://www.midwayusa.com/product/1184126...=ProductFinding