1973 Dart Sport air code?

This is kind of strange. IIRC, the non-A/C cars under dash box had two doors, both operated by cables. On the A/C cars, only the temp lever connected to a cable that exposed the heater core to the air flow. The function lever worked a vacuum harmonica to open and close doors in the box. The only thing on the dash panel that differs between in the little plate where the control levers are showing. All of the other differences are either under the dash or under the hood.

Seeing how the heater hose connections and fan motor are blocked off, my vote is that a PO put something up there to fill in the space. I don't see the R-12 line connections going through the firewall and I don't see the hole for the two vacuum lines (to power the harmonica and to control the hot water valve on the passenger inner fender. The two studs that hold the A/C vents onto the car are no-shows as is the deeper air box the supplies the A/C vents. Furthermore, the A/C code, H51 should appear on the third line from the bottom. The third row from the bottom, reading from left to right should have 1) roof paint code/vinyl roof, 2) Order type, 3) Radiator width, 4) A/C code [H51], etc.

If I were to purchase this car to use on the street, I'd take a close look under the dash to see the heater box. If I can see the wiper linkage on the passenger side, I'd know there is not even a heater in the car. Having made that determination, I'd expect to get a price concession from the seller reflecting what it would cost me to replace the heater and all of the related parts.

Good luck