What should i do for gas mileage el camino gets 10!!!!?

I have a el camino that is a fixer upper it needs a new rear differential and i need to put in and rebuild a 327 small block and then it would be done and ready to drive. with it all said and done i would get about 10 mpg. Thats really bad!!!!!! so what should i do? Or should i just get a little s10 xtreme 4cyl 2.2 liter 5 speed manual trans. getting about 23 mpg. average thats another truck i have been looking at. But i would much rather have the el camino