Best possible mileage?

I am thinking about buying an 84 Dodge Short bed 2wd Dodge pick up with a 225, 4spd O.D. standard trans and whatever rear gear ratio that it would have come with. I am willing to optimize whatever I need in an effort to maximize highway mileage.
What type of mileage is this thing capable of? What could be done to make it the best it can be? I am new to slants, as I only ever had an 81 Diplomat with a 225 many years ago.

Cley