I saw a hot rod magazine a few yrs ago that caught my attention. Ford mustang 650hp 35mpg !!?? They had somehow stuffed a Cummings turbo diesel into it.
I looked on the computer that night checking more into it and found a website 'Fordcummings.com' that specializes in kits to drop 6 cylinder Cummings turbos into the old 70s era Ford trucks. Taking trucks that got 6-10mpg and getting over 20+ with that diesel and tons more torque.
It's not American Muscle, but you might be interested in it anyway.
I make the clutches for this beastie...
https://www.dodsonmotorsport.com/gtr.html
The clutches at the top of this page... The ones with the dots instead of the full ring facing, those I KNOW I made since I'm the only one that runs the machine that those are run on... The others could have been run by anyone at my plant, but I know I made the spotted ones....