72 vs 73 heater boxes

If you are converting from A/C to non-A/C the firewalls are different between the 2. The A/C firewall has a large hole for the blower motor and the bolt pattern will be different as well. The non-A/C firewall will have a smaller hole for the blower motor. The simplest way to fix the firewall will be to make a reducer to install the non-A/C heater box. The "correct" way to fix the firewall will be to cut the non-A?C section out of the Duster and weld it into your 73 Dart Sport. The heater controls and bezels are also different from A/C to non-A/C.

Joe