Gas Mileage query Holley 318

I drove from Ca. back tp Missouri a few decadea go in a 67 Cuda, rebult 383 with 10,000 mi;, 4 speed, 2.94 gears, and a good thermoquad. Interstate mostly at 70, it averged 18 mpg. Longest trip ever I ever made in an old Mopar and only time I ever checked mileage!!!! LOL Usually I just don't care!!
I bet you can do better with a Carter!!!