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

I got nothing... Never tried for fuel economy.. best I ever tried for was pump gas....
I think the 13.9 will be the easy part, the 20 mpg not so much... I'm assuming that's at a steady 55mph?...
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 !