Guy that does my misc machining and fab work I bring in has a 70 Chevelle with a Duramax swap in it. Runs 10 flat and he says its get 30mpg on the freeway. This one here;

https://www.youtube.com/watch?v=SKc_U_Q2s-o

Its a stock truck engine/trans with upgraded compound turbos on it. Be pretty funny to tow a big ass trailer with a Chevelle passing guys up in there fancy new trucks.