My experience with welding cast iron is limited and unsuccessful.
So you haven't done the re-gear job yourself... Just so you are aware, it's very tempting to drop the bearings and the adjuster nut into the open bearing seat, then drop the top cap on to capture the bearing and the nut at the...
The bearing adjuster is pressed mild steel. The bearing caps are cast iron, cut from the base material of the third member and match mated.
Can I ask how you got the threads on the adjuster nut misaligned with the cap threads? I ask so that you don't strip another one in your efforts.