Holley Double Pumper Question(s)

Find yourself a used copy of Holley Carburetors and Manifolds by Bill Fisher and Mike Urich, any edition.
You're buying for a good intro into how carbs work and the diagrams, not the marketing content.
Alternatively for less, the smaller Holley Carburetor Handbook, Models 4150 & 4160, Selection, Tuning & Repair
By Mike Urich