1st, on a truck this old, it is very possible that while it may have had the "dual fuel" option, it is possible that one type of fuel may no longer work if the previous users never used that type of fuel. it is also very possible that parts are missing and the gasoline has gone bad from age.
look under the hood on the side near the fuel inlet port of gasoline,
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.