Sorry to hear about your tractor problems James. If you're not interested in rebuilding the engine yourself you can probably get more in parting it out than selling it as a complete unit. A good loader will go for around $2k in good condition depending on what tractors it fits. Tires and wheels are expensive so those depend on condition. scrap prices are down but it is still a heavy piece of steel so that would add some more to the mix.
If you have the skills and the tractor is OK otherwise I would probably rebuild it. There is no way you will get another one to replace it for the money it would take to fix it. Maintain it (and keep oil in it
) and it will last another 40 years.