Buick's are different than many other engines, they love big carburetors. You can't use the standard formula for calculating CFM requirements. The factory dual quad Super Wildcat had two 600 cfm AFB's and to-date the fastest Nailheads run 2 four barrels on an Edelbrock B262 intake. All 3-2 barrel setups fall too short on CFM's and do not work as smoothly as the dual 4 barrels do. It is hard to beat a pair 650 Edelbrock Thunder Series carbs on a B262 intake with a 401 or 425. A really pumped up 425 can use two 750 CFM Carter/Edelbrock carbs. The 66 Q-Jet intake was the best single 4 barrel intake and should only use a spread bore type carburetor (NEVER USE A CARB ADAPTER), the original Q-Jet was 725 CFM so don't go smaller. Now we have larger square bore carbs so Qjet intake is not as important anymore. The main thing to remember is "go big", if you have a standard 401-425 AFB/ 4 jet Rochester intake on your 401-425, then a 750-850 is a good replacement. If you have a 364 then 750 CFM, 264-322 600-650 CFM . WARNING, 1957-1963 Dynaflow equipped engines will need a special passing gear linkage set up to use any aftermarket carb or you will only get half throttle and you will cruising around in passing gear all the time! check in the induction parts page for picture of that linkage. If you want something that yells HOT ROD, then go with 6-2's or my new 4-2 intake setups; you would think 6 Strombergsgs would be too much but they work great on the larger nailheads ~ run 4 on the smaller ones. We have found that you can get good MPG running them direct, progressive linkage is not recommended. These little 2 barrels are only 150 CFM each. My Martin 4-2 intake can be ordered for 4 bolt or 3 bolt carbs and with the small balance tubes they work great on the street and the cheaper Rochester or other 4 bolt carbs makes it more affordable. You notice I did not mention Holley: we don't like them, because we like carburetors that last and don't cause engine fires! One more thing, Offy 3-2 and 2-4 intakes are not even considered for a performance Nailhead Buick, if you feel your Buick has too much power then install an AWFUL-HOUSER. Good news is we can fix them now, check out our service for correcting them.. About intake spacers or risers: we will not sell them because they do not work. We have found they cost you 10-15 HP and 10-15 Foot Pounds of torque! DO NOT space the intake manifold up. Carburetor spacer plates can work to add power but you must have the hood clearance so you don't sacrifice air filter size and clearance.