Look through Dizuster's old posts on his '62.
It hauled butt with a used 360 & budget turbo, but wasn't built for MPG.
Seems to methat if you don't have to whip an engine to run a given speed that there would be a MPG bonus.
But that's hypothetical on my part from comparing a Slant vs 318 in Darts, all stock drivers from years ago.