Hot water goes to the heater from where it's hottest, at the intake manifold, just before it goes back to the radiator, and is pulled thru by the water pump. So, from intake, to heater, to water pump. If you're going to include a shut-off valve, put that in the line from the intake to stop hot water from entering the heater.

In some cases, heaters will work better if the intake hose connects to the bottom of the core and has to work it's way 'up hill' on it's return to the main system. You may need to play with that and see of one way is more efficient than the other.

 

Yep, all Ford cars and trucks, I think, so top (of engine) to bottom (of heater core).