Gotcha. If I was trying to make 530 at the wheels on N20, honestly none of those would be my choice. Maybe, and it’s a strong maybe I’d use the rpm air gap but not with any of those carbs. That’s just me, I like Holley carbs. And a Holley would be on a good (Victor or similar) single plane. On magnum heads you might be limited to the Indy or M1 for a single plane.