power valve size

You are not getting the point. The carbs are still under vacuum and if you have 6 in vacuum your PV are open at all times, you need to drop to 3.5 or maybe 5.0 but you need to drive it with a vacuum gauge hooked up under the throttle plates not manifold pressure. Now you will know what your vacuum drops to and you can pick a power valve that matches your engine. It's the only way to do it.