If it has a square hood it is probably an electric start model. I would see if it will start, or at least turn over even if I had to jump it off. It's hard to believe it is not worth something as there are people who collect old Gravely tractors. They are built like a tank. I have one I bought new about 27 years ago and it still runs as good as it ever did.

Having said that it would be better sold on Craigs list or ebay where it could bring as much as $200 to $500, or more, but with no more than you know about it it's hard to tell.

A picture would help.