I converted my non AC firewall to AC, by cutting the holes open to adapt the A/C box. The only difference was that my lip around the blower motor is not there. To convert to non A/C, just do as Carl's body man is doing. Cut off the blower lip and weld in a plate over the coolant, A/C line holes, and blower motor hole. Then just cut 2 new holes for the new heater line locations.