[51504bat]

Early Merc pumps used the spacer under the mounting ear on the pump. The earliest ones were wide belt and IIRC used more of a square spacer. The later Merc's were narrow belts and used the U shaped spacer. Mac Van Pelt might be able to provide more definite info on the years of the pumps. FWIW: the Merc pumps aren't repopped.