The crystalline grain structure sounds to me like it might already be a weld repaired part.
Talk to a good gunsmith about doing it right and it's going to be expensive. Same for a machine shop. I am both and
would strongly suggest you find an original fox part or
perhaps repair by welding the one you have.
The very best answer would be find a parts gun , cheap and
maybe you can break even on the whole deal.
I have worked on that part and getting a Fox to open smooth as a factory gun is not easy.
Those little parts are trickier than you might think to make
correctly.
If you must make one I would suggest case hardened mild steel.
Good luck with your gun ...
