So it sounds like you got a good build there.
What type of distributor is on the car. Do you have vacum advance hooked up. Often removed in race engines. If not you can save some mpg right there with a carefully tuned setup.
Multi spark also saves fuel. Smaller carbs can use more gas depending on the driver. For me my foot is in it way to much. Larger carbs make good power so usally your in it less. But not really always the case.
How is the gear. This can be the biggest fuel savings of them all. Even the next size higher could save a few mpg.
Good spark plugs/gapped and good wires. Can all help with mpg. Royal purple light syn oils can help also. And most importantly make sure its tuned right. If its blowing black smoke when you floor it you might be to rich. Did you tune the carb. A dyno tune with wide band may solve a lot of issues. It would suck to change all that stuff and find its only a little better. Or buy a four banger to drive to work and rod for the weekend. Its never going to get great milage its still a v8 sports car.
If you really need to up the milage get an LT or LS engine from the junk yard with trans and computer/wiring harness setup for a swap. You will be suprised how cheap it can be to swap and how much better mpg and power you cna get out of the lt or ls style engines. Ls and 6 speed could put you over 20 mpg and still run low 13 or high 12's could pay for itself in gas milage alone. Also your race motor is probalby worth a few buck in your area.