How do you replace heater core in 1974 Lincoln mark V?

To replace the heater core in a 1974 Lincoln Mark V, first disconnect the battery and drain the coolant from the radiator. Remove the dashboard and associated components to access the heater core, which is located inside the HVAC housing. Disconnect the hoses from the heater core, remove any retaining screws, and take out the old core. Install the new heater core in reverse order, ensuring all connections are secure, then reassemble the dashboard and refill the coolant before testing the system.