I ran one on my 440 for years. I made a circuit that switched the pump and fan from the starter relay to a thermostat relay when the car was turned off. This cooled the heads and block down nicely.
Mine is wired to my ignition (for now) so it runs when the key is on. I also let it run for a few minutes after shutting the motor down to circulate coolant. I've been meaning to wire mine up to a direct manual switch not in the ignition.
The reason not to use a T-stat is that most electric pumps do not have a bypass around the T stat. Up until the T stat reaches temp and opens the pump is running dead headed and cavitating (kills the pump fast). Also once you shut down and the T stat closes (say at 165) the system will develop quite a bit of vacuum as it cools further causing the hoses to collapse (ask me how i know?)...