The hole is near the outer recoil lug....welding not advised. Tempering begins as low as 350*.
Drill hole bigger, tap for a screw in plug, set plug with red locktite; plug already drilled/tapped for the scope mount screw, would work better.....can be done on a lathe...........not a lot of torque on that screw.
Cheaper WECSOG--fill hole with JB weld, drill and tap for scope mt screw on mill. Must be square to receiver centerline.
Cheaper yet..get a quality scope mount, fill receiver hole with JB Weld, coat screw and mount surfaces and screw, with release agent.......clamp mount and screw to receiver, keep JB Weld fully centered around screw...........JB does not run, can be fixed up later on, too, and redo's a snap.
My choice.