Welcome to the forum!  The smart guys will be along in a bit.

I don't think getting a mag cutoff will be too much of a problem. 

Whatever you do don't drill any more holes in the poor thing.  Seems like someone had a scope mounted on it at some point.  Jeez I hate that but the times were what they were.

Check to see if you can discern a filled in hole between the dovetail and the forward screw.  You may have to roll the barrel in bright light just right to see it.  I have a barrel with plugged screw holes and that is how I have to find them.

there may be after market rear sights that that can be pushed into the dovetail.

I'm just spitballing here.