Those are all excellent points. Just another thought if you like a snappy throttle and fast response is to not overcarbuerate the engine.
Holley makes a brand new 2 barrel street avenger that will make your 326 very snappy and responsive. Now from 70 mph to 100 mph you won't have anything,....but that carb is real nice and about 350 bucks brand new.
PJ is right about the timing and rochesters are great if all set up and rebuilt right and you can handle it, but that 2 bbl Holley street avenger is hard to be. We all tend to discount the importantance of the velocity of the air pulling through the Vacumn Venturi of the carb...
That velocity makes a strong draw on the mixture and creates a very snappy throttle response,...of course as PJ said timing etc must be correct as well. But a engine overcarbed, ez to do on a 326 will be sluggish as the air has no velocity through the centuries, just sort of passing by slow and it effects everything, undercarb a little,....too big won.t help.
Racers and guys with stroked 455 killer engines giant valves etc they need big volume carbs. As far as Vacumn, really depends on needs, power brakes? You have an auto trans modulator, Vacumn blend doors and should have full vac to distributor. You can tee those off pretty ez.
Make sure you have an operating PCV system as well....!
You will get it and that 326 will surprise you!