Welcome aboard Peter.
I haven't seen that frame mod before.� Damaged frame repair or plow Jeep mod are both good guesses.� It's just a strange place for a 3A frame mod.� Plow jeeps usually get beefed up more toward the front frame horns, and this is the strongest area on the 3A frame, so it's not likely to break here.�
As Nate mentions, a 3A frame is made much stronger than a 2A.� Even with the heavy pitting, it is probably salvageable, but I would give it a few good whacks with a hammer prior to paying for the sandblast work.�
Also, depending on your welding skills, anything can be fixed.
Tim