Grind or file the weld flush with the flats, then drive the sight out. Sacrifice the sight when removing the welds, not the barrel. Now you can see just what you have, and decide if a fix is in order.
I expect it is not as bad as it is ugly and can be cleaned up quite easily. Those are small welds,quite far from the bore, and it should be easy to re-work the dovetail to new condition, or enlarge it to the next size.
Pete