Odd Suspension Issues

In my view, That second divot in the finger was created as the bolt was turned with a wrench with vehicle weight on it. A ball end in a ball cup has much more surface area and a dab of grease, preventing this. No turning or additional wearing happens while driving, so the original proper cup doesn't grow larger. And weren't not supposed to adjust while vehicle weight loaded. I'm kinda surprised that you haven't already stripped threads. Aftermarket has new bolts and nut blocks because this happens.
Welding would only fill the extra lil divot at best. It could make this piece of forged iron more brittle. I would inspect the threads but if all is good just put it back together correctly and set the right height correctly, i.e. lift, adjust, lower, jounce, measure, repeat.
p.s. A single separate lower arm with that sway bar attach tab on it would be difficult to find ( like those forward bar mounts ). Any A-body lower arm would work, You would cut, move, and weld your tab on it.