Everything can be reached from below. The body has nothing to do with it, except for the top of the bracket in your picture. There are two 5/16" bolts (1/2" head and nut) on each side that secures the bumper bracket standoff to the body that are reachable from the top of the body rear crossmember (where a rear spare tire bracket is or would be attached. BTW, there are three more bolts on each bumper bracket further inside attached to the frame that need to be removed if you want to remove the bumper brackets/arms. Another BTW; there is suppose to be a rivet that secures the bracket in your picture to the bumper bracket arm, not a bolt like in your picture, if you want to make it look correct from the factory.
Rusty Nelson