Recently replaced blown head gasket. Had head professionally plained and valve seals replaced. All new gaskets, new thermostat, new temperature sender. Fan came on when needed now. Adjusted valves, cleaned carb. Finally managed to set the float so it is not leaking anymore.

Engine was running great, good power, nice idle. Yesterday went to the field to talk to the custom guy who was cutting our grass. Normal drive, no race. When I came back to my shop I remembered to top off the radiator with coolant as I had seen the day before it was a little low, just visible. When I took the front cover off, engine suddenly died. So I tried to restart it, had to give it a bit throttle to start, and it was smoking badly from the exhaust. White smoke, smelled funny. Now there is coolant leaking from the exhaust. Where the first junction is right in front of the head.
What happened? Head gasket blown again? Valve seal? Man this sucks. Have to open it up again...

 

If coolant is dripping from the exhaust then yes I'd say blown head gasket. Plus if radiator was low I'd check around the water pump weep hole for signs of a w/p seal leaking along with the impeller for any damage to see if that was the cause of coolant loss.Even trapped air pockets in the cooling system when you had it back together and if not fully bled of air can cause one to over heat quickly and can cause head gaskets to blow.Also on these 500 models the head torque sequence is critical.