Small Block Carb and intake ?

I am gathering parts for my 67 273. I have an original 4 barrel intake and I am pretty sure I will get a Edelbrock 500 or 600 cfm to go with it. My question is this. Will the edelbrock need a spacer plate between the intake and carb for butterfly clearance? I am going from a two barrel BBD to the 4 barrel set up. My VIN number indicates the car came with a four barrel and was the HO commando. What increase if any can I expect with a four barrel. I have stock manifolds and true dual 2.5 exhaust with crossover and Magnaflow muffs.


John B.