cut out the section where the nuts were in a nice rectanuglar shape, then take a piece of 1/4in plate or something there abouts cut it to the same size as the piece removed. Transpose the location of where the old nuts where onto the new plate, Drill holes, weld nuts over holes and then weld new plate into place.
Do the exact same thing but with the old plate, cut nuts off, weld on new nuts, weld plate back on.
I would only consider welding the bracket to the frame as a last resort, this is an item that wears out and needs replacing on occasion. having to cut welds would not be fun. If its a pure trail rig, then weld that sucker up.