Ms. EarleJ --
I'm very sorry for your loss. I'm also sorry that your mower fellow won't show you how to operate such a fine machine. It's really not that difficult if you are familiar with standard transmissions of the age, but that's another issue.
Serial number 9N500 is an early 1939; the first 1940 (in my reference book anyway) is 9N10234. My 1940 is SN 9N35421 and the bill of sale is dated 20 August 1940. In any event, the 1939s had an aluminum hood -- assuming yours has not been changed for some reason test it with a magnet -- if aluminum the magnet won't stick.
If yours is indeed an authentic '39, don't let it go easily. Around here, if the bidder is knowlegable, one will pay $ 2750 - 3250 for a running condition '39, approaching $ 3800 for a restored true '39. Of course, each area is different. For comparison, 1940 and newer 9Ns and 2Ns are selling at auction here for $ 2250 - 2500 for a good runner, maybe $ 3000 for a restored unit. In my opinion, the low SN should inflate the price at least $ 500 from what similar condition newer 9Ns are bringing.
I'm afraid I can't help you much as far as a place to market it in your area, but you might consider calling the folks at N-Complete. They specialize in restoring & remanufacturing models N and I'm sure they'd love to get a solid '39, but I haven't a clue how well they'd pay given the distance. They're at n-complete.com.
Too bad we aren't closer, I'd love to have a good '39. Good luck,
Pete P.
Harborcreek, Penna.