Since they're already unsightly and have ruined the collector's value, I like the idea of threading screws in the holes and grinding and filing them flush inside and out. I have seen some well done examples of this. More controllable than welding unless you are very skilled. That's assuming you can find the proper screws to fit the threaded holes.

From what I understand, the pressure of the 30-40 Krag round in the chamber would not pose any risk of damaging the receiver where these holes are drilled. If you're concerned, leave one open and any excess pressure would be vented out the "escape" hole. I think that would be unnecessary, though. The strength needs to be forward of the closed bolt and where the lugs engage the receiver, not on the left side of the receiver.

Good luck. We'll see what others think. I have never done this but have seen some crappy repairs and some wonderful ones.

Is that a 4 digit serial number on this receiver?