Before you say what the heck does a Texan know about block heaters note the "adian" part of my name. Used to spend my winters in Canada too.
Most northerners will say the best block heater is an external tank type heater connected to the engine with heater hoses. High wattage types are available that will heat the engine in an hour. The tank inlet should be teed into the lower rad hose; tank outlet connected to the rear of the head. If your tractor is a diesel, the very back of the intake manifold has a port that covers an opening into the head water jacket. Very early 65 to 70 4000's dont have the port, it can be drilled and tapped. If it's a gas 4000 it has a water heated intake manifold and the heater can be connected to one of the ports in the manifold water jacket.
Second best appears to be the type of heater that replaces a frost plug. They're lower wattage and need to be plugged in to 110V longer.
Third is the type that splices into the lower rad hose. They'll work but aren't adequate for really cold temps.
Forget about oil dipstick type heaters.