Carb size ?

Holley 80453 (390 CFM vac sec) works well for mild to moderate 6 cyl builds. A 500 AFB/Edelbrock or 470 Holley Truck Avenger would do well if you have are running a mild cam and headers. The Holley 570 Street Avenger will be able to support just about anything a street /6 will ever do, but it would be overkill for a basically stock or really mild engine.