What mileage does your slant six powered ride get?

Stone cold stock 1964 Valiant V-100. 1964 Mobile Economy Run from LA to NYC, average 23.0851 mpg over 3,243.8 miles. Combination city and Highway. Easily mid to upper 20's if not 30+ mpg cruising steady on a flatish highway.

https://www.hsmichigan.org/wp-content/uploads/2012/08/Mobil
the OD gear is more like a 5 speed with No 4th. when doing these averages, its at 55mph should be No or No less. when you increase the HP on a motor, you most likely substitute mpg's. or go over 55 mph.