[Chucks72Longbed]

I would start with a 3/8" x 16 starter tap. The beginning threads on the tap are tapered enough to get into the good threads. Then you should be able to tap with a #2 or bottom tap to clean them up. If that doesn't work there is plenty of material around the bolt hole to jump to a 7/16" or 1/2". Carefull, don't go any deeper.