Rallye Gauge A/C ?'s

I've got a HVAC box out of a 73' Duster that I just rebuilt with new seals and cores...and I have rallye A/C controls from a A-body Barracuda, the push button style. I've seen some A/C units in Dusters have only 4 buttons, where as my setup has 5. Does anyone know the difference in these two units? I'd like to make the barracuda controls work with my 73' box.