Actually the early OEM pumps were 6 bolt, and the aftermarket pumps are 5 bolt.
Just a FYI. the factory pumps had a 5/8 inch thick rotor, where the replacement pumps, have a 7/8 thick rotor. So the replacement pumps are a high volumm replacement. If you get a high volumm pump (which is not needed or really wanted), the rotors are either 1 inch or 1 1/8 (I forget which).