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

YY1 said
Starting with a Magnum will make both goals easier.

Staying with a roller cam should, too.

About 6 years ago we went for 13.9's with a stock converter, no headers, and 2.45's in the '76 Duster. We made it, but that was a 360 and we didn't check mpg.