The bolts come up from the bottom and the nut is caged so it couldn't be for attaching the body mount, unless to replace the caged nut. My guess is they are there to catch dropped washers or tools ,which rattle under there, and in turn cause the owner to search for hours to find only to be discovered forty years later by the fifth owner who couldn't hear the rattle as he's half deaf. In my case it was a screwdriver which I still have if the original owner is still looking.
