Coolant flow to heater core?
This is from 67 dart Coronet charger FSM
Outlet of heater core is on driver's side (Left hand drive car)
Outlet goes to water pump.
Here is a Dart specific image.
Same driver's side outlet and water pump connection, just hose routing is a bit different.
If I'm not mistaken the 67 Plymouth Suppliment is the barracuda FSM
MyMopar - Mopar Forums & Information - Service Manuals