1978 Chevy Truck gas mileage

I have a 78 chevy c10 p-up w/ a crate 350 stock, long headers, edelbrock rpm dual plane, dual exhaust, 700r4 tranny w/ a shift kit and 2400 stall. Stock rear, no cam, holley 600cfm street vac sec carb. I am only getting 10 mpg city. Is this normal? Should I ivvest in a fuel injection set up? Maybe a holley commander 4-bbl 700 cfm tbi? Any tricks to squeeze more mileage w/out killing the performance. Thx steve