63 c-10

ok i have a 63 chevy c-10 that has a sbc 400 and three speed and im trying to build a truck that gets good gas miliage and just wonder if anyone had any sbc tru ck that gets 18 or more mpg and what kinda set up you are running cause i have a lot of resorces and im just trying to have a old school truck that is more driveble