This C60 will basically be going back and forth 3 miles hauling wheat to silo on a gravel road.
Buy a set of Chinese-made tube type bias ply tires, the same size as the ones that are on it now. They should last 20-something years at least, and the sidewalls will dry rot long before the tread wears out. You probably won't even get them warm enough to iron out the flat spots that develop from being parked for a few days at a time.
Jerry