Smallblock efficiency or How to have your cake and eat it too

A lot of stock 340's got 20 mpg back in '68 and '69.They really are the best all around engine in an A body!
I know a lot of guys with big blocks, big and small strokers or nasty small blocks that won't go to cruz night get togethers if they are more than 6 or 7 miles away just because of poor mpg.