i have a 1985 f150, 4x4,351w,4bbl shortbed. ive already put 6700$ into the truck, i wanted to upgrade the motor/rebuild it, was looking to see if it would just be easier to buy a crate motor for $6k, or rebuild it. also i was interested in how to find out how to identify the heads that are on it. it says 32 right where the valve cover is, not under it just next to it.and i also get 7mpg- ne ideas as to why?