At this point I would try and punch out the welded nut out of the frame with a BFH (Big F...king Hammer) and good punch then drop in a bolt from above.

Attempting to remove the broken bolt again means trying to get the broken extractor out...which will not be easy, there's no drilling it out because it's hardened steel and much harder then a any drill bit, the only way to get it out is using a diamond Dremel bit and grinding it away, if by chance you go this route and get the broken extractor out, drill the bolt again with several drill bits going up in size until you get to the size of the original bolt or slightly bigger and then retap new threads.