My tow truck has a 350 V8 with a 2-barrel carb and it will run 65 mph all day long! With that said my truck only weighs 10,400 pounds and I almost never pull anything. I'm guessing I get about 6-7 mpg.
I also have a 322 Buick Nail Head V8 in my Fire Engine and I've driven it over 30k miles going to shows. It runs very well at about 63 mph turning about 3700 rpm and gets 6.8 mpg. It weighs 14,200 pounds.
Your truck was available from the factory with a V8. Valve covers will be close to the fire wall, tall covers will not work without body wody to the fire wall.
I say wind her up and see what she'll do! BUT before you do that FIX the hydrovac, it adds about 900 additional pounds of stopping force in the brake lines. To test if it's working, on your first engine start of the day, step on the brake pedal and hold it with medium leg pressure, then start the engine...as the engine vacuum increases the pedal should slowly move towards the floor, if it does it's working.
Mike B
