High Performance muscle car modifications

Rebuilt 85 Monte Carlo SS needs engine tuning/modifications to make it able to be driven. Current specs burns through gas too quickly. Motor was built from a small block Chevy. Top is high performance heads, cam, 3" exhaust and 650 cfm Edelbrock carb. Has electric fuel pump and is currently geared for 1/4 mile run. Vehicle burns through gas very quickly. Want to modify engine/gears to make it able to be driven longer distances. Literally burns through 1/2 tank gas in as little as 20 miles without carb spillover.