I have always used the water pump port ,next to the lower radiator hose for 1 and the intake fitting for the other.My logic was that the water pump pulled the water from the hot engine before the thermostat ,thru the heater core .This method gave me the quickest heat.I have been in cars that the heater blew cold untill the first time the thermostat opened and did not like the wait.Also the feed line into the heater core needs a restrictor if you are gunna get on this motor or most of the time you will pop the heater core when you get on it...hope this helps