Yes there are 2 versions, I have 1 of each versions of the Holley 3 barrel carbs the 950 with the boosters in the secondaries, and a 1050 that has dump tubes in the secondaries instead of boosters. When you look at the secondaries you will see that the boosters and main air bleeds are closer together than the primaries. The rear gasket, metering plate and gasket, and diaphragm for the vacuum pod are all one offs for the 3 barrels only and are getting harder to find.