Until you change the camshaft, you will not change the engines air flow demands or appetite. Cylinder heads are useless without a cam, as the cam is the link to the engine for the heads.
I hold the record in the camshft department for the quickest and fastest naturally aspirated 302's in the world.
If you have a stock cam in there, that carburetor is dead wrong for you and is costing power. It's not all about CFM's. CFM's are worthless if a carburetor does not vaporize fuel well because all of the air flow into a cylinder means nohing if it can't burn. Carburetors are set apart in power numbers by how well they vaporize fuel. This is where the boosters come into the picture. Get them to vaporize and the burn speed is much faster which makes the spark advance requirements much less. When you do that, torque goes up everywhere and BSFC comes down. I.E. power goes up but fuel demand goes down. Hell of a deal..!
If you ahve a stock cam in there, I am going to suggest that you are making around 250 horsepower at the flywheel. Put some rocker arm pedestal shims on that thing. That will be a very cheap and effective tweak for you.