If you put a o2 sensor bung in the exhaust we can meet up with my lm-1 and tune the car. But as for mileage you need to lean the carb out, not fatten it up like toms did for performance. The 650 is not too big. I ran a 750 3310 on my sub 8:1 318 in my duster with 3.91s, weighs 3600 with me in it, and had a summit cam larger than the one you listed and it got around 18.
