Gas price going up // Rethinking the new project car

I have pondered an early Dart or Valiant with a slant 6 or 273/318 with a 833 OD as a daily driver . It would be fun to see how much MPG you could eeke out of it .
I just like to drive the old cars ... I have a Ram 1500 that I drive in the winter and a BMW Dual Sport that I ride in the summer . My Barracuda is my main passanger car and I will even drive it in the winter if the roads are clear . The Barracuda has around 390 hp but I rarely floor it . Probably use under 250 hp most of the time . So whats wrong with someone wanting to build a Mopar that gets great mileage but isnt a 10 second ride ?