How do you replace a heater core in 1965 Buick Riviera?

To replace the heater core in a 1965 Buick Riviera, start by disconnecting the battery and draining the coolant. Remove the dashboard and any components obstructing access to the heater box. Unbolt the heater core from the heater box, replace it with a new unit, and reassemble everything in reverse order. Finally, refill the coolant, reconnect the battery, and check for leaks.