I'm assuming by "quad" you mean any 4V carb, not just a Quadrajet. In general it's not easy to convert the linkage on any of them. Unless this is a strip only car you don't want manual secondaries anyway. If the secondaries open before the engine is ready/able to handle the extra fuel, it will just bog the engine. Vacuum secondaries prevent this by slowing the opening of the secondaries. They will open as fast as the engine can handle the extra fuel/air mix. Vacuum secondaries will provide as much power as fast as manual if the carb is tuned to the engine correctly. If the tune is off a bit, the vacuum carb will be quicker.