I worked with the FFA on restoring a 1942 Farmall H and that had the small fuel tank also. As has already been mentioned here, the small tank held gasoline and was used for starting the tractor. As soon as the engine was warm enough, the gas was shut off and the kero. was turned on. The  fuel line of the  small tank was T'ed in to the line of the main tank at the sediment bowl so that both thanks used the one bowl. The Manifold was larger than the straight gas model to preheat the kerosene as it was sent to the cylinders. I am not so sure it was any cheaper to run the kero. nor was there any more power. It was mostly a matter of fuel availability in so many of the more rural locations. Kerosene was already on the farm for kitchen stoves and lighting (lamps and lanterns)
I don't think it hurts to run on gasoline but it would be a novelty to be able to have the option of the multi-fuel use. The FFA kept their tank, but it was not used.
 I am sure you are in for an interesting project!
               Cal