Dont go too lean in quest of gas mileage at the expense of exhaust valves. Nothing against the little progressive "pinto" carbs with the fancy name, but a single one on a grand champion dump truck motor is an odd concept. Not knowing the venturi sizes of the progressive 2 bbl.- I wonder if it has more or less venturi area than the 1-5/8 stocker. If not then a 235, or even a 216 stocker would be viable too ( but a bird in hand logic is hard to beat).
