What do you want to check? N series serial numbers are stamped into the engine block and both 2N's and 9N's start with 9N........ If it is a three speed, it's a 9N or 2N and at this point, there is no real distinction between them. And whether it is a 1940 or a 1943 tractor hardly affects the value. Post the number here if you want someone to look up the year and model. Be aware that many, many of these tractors no longer have the original engine block.