The N series Fords include the 9, 3 and 8 series, in that order. The number represents the first year of manufacture, 1939, 1943, and 1948, respectively. A 1945-manufacture tractor would actually be a "3N", with a few wartime shortcuts being made from the 1939 models. The 8N can be identified pretty readily by its 4 speed transmission- - - - -the 9N and 3N models only had 3 forward gears. I've got an 8N stashed out behind the barn, waiting for a ground-up restoration, along with a 1936 Allis-Chalmers WC model.
Jerry