Although the 3310 780 Holley was originally used on the 375HP 396 Chevy, the 3310-1,2,3 etc are all later "universal" carbs. I have a few each of the 3310-1 and -2, and on mine, the -1 has the downleg booster and a secondary metering block, with jets, but my -2s have straight boosters and secondary metering plates (no changable secondary jets. Most -2s that I have seen had manual chokes, while the -1s had automatic chokes.