My dad has a M-670 and a U-302 that are close to the M-602. the M-602 is the predecessor of the M-670 and in the condition you described it, I would not pay more than $2,300 for the tractor. But that is considering if it runs. If you decide to buy it and then to fix it up to sell, it should be worth about $3,500-$5,000. If the loader works good and the cylinders don't leak it should add another $500 to $1000. You may get more for it depending on if its painted up or  other mechanical work. I'm assuming it has a torque. If it doesn't work it drastically lowers the price. the plow I'm not sure what that would bring, but in previous experiences in a good to fairly good condition it should bring about $500-$700. 

Sincerely, Joe Reusch

If you have anymore questions just e-mail me.