If you have a 318, just build the 318. As mentioned on here many times, a well built 318 will do just about everything you want it to.
They can make 400hp with ease, get good milage, sound great and be a lot of fun to drive. A good clean-up on a set of 360 heads with 1.88/1.60 vlaves, good cam(voodoo is my goto hydraulic cam), small 4bbl carb, dual plane intake, headers and the like, you wont be disappointed.