318 heads. whats your route??

I am building a 318 using magnum heads. The stock cam that came with the short block is .373/.400 and 240/248 according to Mopar info. With the magnum 1.6 ratio rockers, the lift changes to .387 and .427 and duration changes a little. The tranny is an a999 from a D150 with low gear set, and the rear axle is an 8.25 with 2.45 gears and suregrip. I also have available an a500 OD tranny and 3.55 gears as an option. Exhaust will be a large single pipe, no headers, for the carb, considering a small holley 4BBL or a thermoquad.
What kind of cam should I use to get a mild performance increase without sacrificing gas mileage much? I like lots of passing power/torque in second gear, when I need it, but racing is totally out of the question.
Is the stock cam good enough considering the much improved flow of magnum heads?