How do you replace heater core 1965 Chevelle Malibu?

To replace the heater core in a 1965 Chevelle Malibu, start by disconnecting the battery and draining the coolant from the radiator. Remove the dashboard and any components obstructing access to the heater core, such as the heater box. Disconnect the hoses from the heater core, remove the core from the housing, and replace it with the new unit. Reassemble everything in reverse order, ensuring all connections are secure and refill the cooling system with antifreeze.