Could it be a Classic barrel screwed on? That would explain the proof mark location and no sights. It wouldn;t be set back with the proof mark on top unless you have one heck of a big exctractor cut.
Also the '300 MAGNUM' stamping doesn;t quite look correct. It looks stamped rather than rolled. the Caliber markings I thought were the exact same font and size as the MODEL 70 - that precedes it
