Size carb depends on how well the whole package breaths, and how you intend to drive it. On my 496, i have a 3 inch exhaust, 2 inch headers, and ported aluminum heads, and a .625 solid roller cam. Since I play on the street only, an 850 Holley with mechanical secondaries makes all the power I need. Without knowing your whole combo, including tranny and rear end gears, I'd say a good 750 Holley will do you well to start with. It will cover you up to and over 500 horsepower, and give you good throttle response on the street, especially at the stop lights!
