I've benn running a 650 holley on my 311 GMC racing engine. This is only my opinion but I converted it back to a vacuum operated secondaries. Still a double feed. I figured the engine was a lot smarter than I was. Played with the vacuun springs a bit and went 157 at El Mirage in a roadster. Keeps the tires from breaking loose. A six cylinder keeps a good vacuum signal especially with a 4 " stroke. I was able to run 155 with a Braswell 2 barrel with annular discharges. It flowed 700 cfm but I needed more atomization.
If you use a Carter/Edelbrock style carb you can lighten up the weights on the rear butterflies for performance and they don't leak..Good Luck
