Charles,
The Holley Double Venturi is also correct. There are two styles of Zenith, the very early and the 2nd generation which has the boss and pin on the front side with the unused boss on the back side, the "Z" was also moved to the front side of the upper housing.
I have a rebuilt Side Bowl and also a rebuilt Holley Double Venturi. I will sell these outright with no exchange. If interested send me a e-mail.
Ron in Quincy (CA)