A rough rule of thumb: if you want more power, open up the intake side of things, if you want better gas mileage, clean up the exhaust. The shorter the cam, the more cylinder pressure you'll get. An RV type cam uses "faster" ramps on the lobes and manages to lift the valves a decent amount with less overlap. Porting will give you more power and gas mileage when done with that in mind. Free flowing exhaust manifolds or medium sized headers with a decent exhaust system including an H-pipe will also give the best of both worlds.

Proper tuning of the final combo is critical. Getting the right mechanical advance curve will give you the best power, and a properly adjusted vacuum advance curve will give you the best mpg. Jetting the carb (as you noted) is very important as well, gotta be lean to be green (or save as much green as you can) under light-medium throttle.

Next, the right gear will get you off the line and rolling more efficiently, and a lock-up convertor in an overdrive transmission should make you the mileage champ!