I don't know of anyone who has done this yet. The entire family of WSM cartridges has some unique feeding issues - problem is that, in the process of figuring out just how to do this, you could screw up a couple of actions. You would certainly need a WSM magazine box and follower. You could duplicate the rail width/profile of a Winchester Model 70 in one of the WSM factory calibers. Bolt face and extractor are pretty basic. Then the issue would be whether the controlled feed extractor on the Mauser would be compatible with the somewhat steep feed angle necessary to chamber on of these short, fat cases.

Personally, I wouldn't do it. Just buy a factory gun, or re-barrel an existing .270 or .300 WSM.