Im running a 323" 4spd 4dr with 3.23 gears, and the 340 cam. 1.88/1.60 valve 318 heads 8.8:1 compression. The best 318 mileage manifold is the singleplane Edelbrock "streetmaster 318" intake. It is a 0-4,800rpm band intake made for better mileage and stimulating vacuum. I found an old 770 SA holley with a stiff secondary spring really works excellent. I tune with a vacuum gauge, it diagnoses what you need to see.

Use the lightest wheel and tires. my 225/60 on steels weigh in at about 14# a wheel.

i get about 14MPG with everything. The biggest trick is the 1st to 4th skip shift.

20 MPG driving around is near impossible.

A edelbrock AVS is a excellent street carb.