The Model N has many improvements. Magneto, governor, water pump, etc. The engines are similar and the N engine can be put into an F. In fact the basic engine is the same until 1952. The Model E27N added a starter in addition to the N's improvements.
The N was legitimately equipped with rubber tires as an option. I doubt that the F was, except maybe hard tires in the industrials. The N has quite an attractive color scheme. For the most part, the F was made in the USA. The N was only made in Ireland and England. Close copies were made in Russia.