Engine size recommendation

I would like to have a set-up closer to 15-17mpg, is this possible with a 360? Is it possible with the 318?

I won't be racing anyone, I want a strong reliable engine that will for the most part be a daily driver w/ the exception of bad weather. So in order to invest the money I want to take the fuel efficiency into consideration, especially with climbing gas prices, but would still like a little pep to the gas pedal if I needed to pass someone. If the 318 is the only way to accomplish this, would simply rebuilding it, new bearing, seals, etc. and adding a 4bbl intake/carb (any suggestions for best combo), headers with dual exhaust do the trick. I'd like to have a good idea of what I want to do with the engine before I engage someone to rebuild it so I can explain what I want to have done.

Thanks again for everyone's input, it is much appreciated.