Yeah, so this carb is prior to the quadrajet. Online info shows 3 different sized cfms available. The carbs I have have the same size primary and secondary bores, 1 1/4" if memory serves, and was rated at 486 cfm. The 2 jet bores were notably larger at 1 5/8". There are larger 4-jet carbs noted, these have slightly larger secondary bores and were presumably used on bigger cubic-inch engines such as Buick and Cadillac of the era.
The secondaries on these carbs are interesting - they are physically mechanical secondaries, but there's an additional set of spring-loaded butterfly valves that sit above the secondary throttle plates. They only allow flow through the secondaries if there is enough airflow to open those butterflies. The tension on the springs were factory set; there is a set screw that can alter that setting, but I know nothing about how that might be calibrated/adjusted.
