you can test the radiator at your house.
pinch off top hose or remove hose and leave cap on.. feed one of them, either cap or top connection with a 1/2" garden hose.
take the lower hose off.
a good rad should be able to take flow from a half inch hose. if it can't. it's plugged.
as for the water pump test.
hook rad back up, fill with water, block too.. etc.feed water hose into top hose connectionon rad, leave cap on, aim top hose into bucket, make sure thermostat is out.
start tractor. water pump should make flow out of the top hose. you can feed it some water via water hose first to make sure it is burped.
Lastly.
Is it overheating via gauge, or simply spitting at cap?
have you checked for a blown head gasket?