318 build #2 "cost minded" for the '74 Duster

20 down our single highways, going through small towns. I think 13.9 will be the tough part with the 318 because of the 2.94's, stock converter, and no headers. And trying for the 13.9 will make the 20 mpg a tad difficult as well. email says another package should be in today !
20 mpg seems like a lofty goal. What did the six cylinder feather dusters get? How heavy is your right foot?