How do you install heater core in a 1970 Chevelle with ac?

To install a heater core in a 1970 Chevelle with AC, first disconnect the battery and drain the coolant from the radiator. Remove the dashboard and the AC housing to access the heater core, then disconnect the hoses and remove the old heater core. Install the new heater core in the same position, reconnect the hoses, reassemble the AC housing and dashboard, and finally refill the coolant and reconnect the battery. Ensure to check for any leaks after starting the vehicle.