[Oldsguy]

I think GM has used the method C.J. described to mount the rear bumper since about the mid 70's. I had a '77 Delta 88 with a bumper mounted like that and the bumper fell off. It was due to dissimalar metal causing excessive corrosion at the mounting plates. The plates were steel with another kind of steel bolt and the bumper was some kind of aluminum. The bumper basically disintegrated. I don't know what the bumpers are made of now but I bet there is a similar situation because I know they still used the shocks in the eighties. Don't mount the hitch directly on the bumper. Just my 2 cents based on experience.