Diff. mounting bolt stripped!!!!

[hilux30]

I pit in a LSD in my S13, so naturally I got the longer bolts, and the passenger side went in no problem, tightened up and the BAAAMM just kept spinning. First I thought The bolt on the on the other side (inside the subframe) broke and just spining, but no the thing is smooth with no more thread. since were the bolt is it's like a plate welded to the subframe, thinking about cutting the welds, weld a new bolt and then reweld the plate, unless someone got a better Idea, thx in advance