The small 20hp Simplex loco was used a lot in WW1, and developed into one of the most common narrow gauge locos used in industry. The original WW1 version had small variations, and quite often was modified after the war. I have based model on various drawings and photos. uses a Tenshodo 28mm wheelbase chassis, with screw fitting under engine cover. Room for small amount of extra weight. No couplings so choice is up to modeller.