How to install a 1968 Chevelle heater box without ac.?

To install a 1968 Chevelle heater box without AC, first remove the old heater box by disconnecting the heater hoses, unfastening the screws securing the box to the firewall, and detaching the control cables. Clean the firewall area and ensure the new heater box is compatible with non-AC models. Position the new heater box in place, secure it with screws, and reconnect the heater hoses and control cables. Finally, test the heater operation to ensure it's functioning properly.