best bolt ons for a 318

Well, lets see, the basics are covered. What intake manifold is it exactly?

Is it a fully converted ignition system? Coil included? Did you open up the plug gaps? You very well could open them up to .055 and still not only run well, but gain a minor amount of mileage. (OK, it's pushing it, and very small, but everything combined should show a gain.)

What fan is in use? The best mechanical fan is a Viscous fan from MP. Or use an electrical fan for less drag on the engine.

I think, from here, knowing your gearing is the next key to the next move. Power or mileage? OH, also, what year is the engine? Is it bone stock now on the inside? (Changed the slugs?)