I don"t believe they were call dual fuel. They were all (what we called tractor fuel burners) The small tank was not to be used for all day running., just to start the tractor and use until tractor was warmed up. When my Dad bought a new gas burner LA in 1948 he than just used gas in the L . he never changed the intake manifold and the L still has the fuel manifold on it. This L still has the original Kinston carb on it. Picture is of my L new in spring of 1929. Note the manifold.