Carb help '30 sedan SBC

Just got my first streetrod...1930 Sedan. Has SBC. Don't know engine size and engine code didn't help. Don't know rear gearing either. It presently has Edelbrock Streetmaster manifold and Edelbrock 1405 man choke carb. Car runs fine etc but is definitely not a 'tire turner'...but I am ok that...I just use it for cruising. Problem is it gets horrible mileage...8-9 MPG.

I just ordered a new manifold-air gap type-because that might help with heat issues when hood is on. As a matter of fact, having the hood off not only helps with heat problem but also helps with mileage issue (1-2 MPG better). (Engine doesn't overheat, but the carb pulls in air that is too hot).

I was thinking of going to an Edelbrock 1406 as that has elec choke and apparently more tuned for economy than 1405 (according to Edelbrock page)...both are 600CFM carbs.

What are the chances the engine is over-carbed? Should I go to a 500 CFM carb...like the 1403?
Any ideas and input appreciated. I know nothing about this stuff so don't get too techy on me!
thanks