Gas Mileage query Holley 318

Jason, 'coz your in oz.....
When I got my GTO, 3700 lbs, with a tired 389 engine, 2 speed auto, 3.08 axle, I fitted an Mopar 850 TQ & elec ign. I got 23 mpg going from Sydney's north shore to Gosford, about 40 miles. Slow moving weekend traffic getting out of Syd, up hill down dale to Gosford.
That is about 20 mpg in US gallons.