I'm with Jim regarding size. However, you can call Holley tech support. They'll calculate your need based on Cubes, RPM, and volumetric efficiency...and probably come up with the same reccomendation. Not so critical on a vacuum secondary carb.

You may want to reconsider the manual secondaries. I've been advised that they will affect drivability on a "heavy" street car with an automatic tranny(our 'birds aren't considered light in weight). If you're building a racer, do it!