It would be better to let the welding shop repair it if they would be willing to do it.
Or a machine shop.
It may be expensive, but a lot cheaper than a totally messed up crankshaft.
I would be willing to bet that they tried to loosen that nut while they had everything red hot, that's why metal gaulds,it would have been better to let everything cool just a bit before turning it, the same applies to the cylinder glands that need heated to break loose, I have seen a few of those gaiuled also, same situation, turning it while everything is close to melting temp.Okay. Yeah il take the crank in to a machine shop. See if they can clean these threads up.