It looks like an original Mauser Oberndorf bolt, it has part of the proof marks left, can't tell if the rest were cleaned up after welding, or to remove rust. It is not numbered to the action, anyway, so it was "born" with another rifle. I'm not one that goes crazy over mismatched numbers if the action has been or will be rebarreled. It will be headspaced to the new barrel, anyway.
Mike