I'd bore out the hole to a size a bolt would go thru...then look for a way to insert a NUT with a handle welded to it.. The handle would serve as a wrench holding the nut in place while torquing the bolt.. Many trailer hitches and nerf bars are installed thisaway..
You must search for a hole to insert the nut and handle into..or make one yourself if the frame is toatlly boxed.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist