Slant Six mpg's?

I got 27mpg in the 67 dart on a road trip once. I never pay much attention since it doesn't get driven much. But I was a little shocked it did that well. It has about .115" shaved off the head, hooker headers, 2-1/2" dual exhaust, 600 holley, lots of timing, 904 and 7-1/4 stock rear. I'm currently converting it to a 833od so that will be cool to see if it improves over the auto.