In the meantime, take pictures and email them to 3-4 machine shops/welders and see if someone will quote you. Send better pictures than the ones you posted here earlier though.
I'm thinking if you are able to just grind away and re weld it wont cost too much money, but if a welder tells you that you need to chop off the neck and weld it back on, you might be able to find a bare titled frame cheaper than what it would probably cost hourly.
Any welder should be able to the grind and put down some stronger welds, they might refer you to someone more motorcycle specific if the neck needs to be cut off completely....but like i said, in that case, it may be cheaper to find a titled frame and swap everything over.
Me personally, I would junk that #$%*er and find a new frame for 150-200, sounds like you have time during motor rebuild to find one.
Edit: properly disclosed, someone would buy that titled frame from you, like a chopper or rat bike guy.