Is your timing set right on the distributor? I redid my WD45 a couple of years ago and the first time I ran it, it ran hot and discolored my double wall chrome pipe. Found out the timing was off and once we got it back in time I have had no over heating problems since. Please excuse my ignorance if the tractor has a mag. I"m not very familiar the model C.
P.S. - I swapped to electronic ignition which caused a large change for me.