I just finished a Classic Auto Air install on my '69 Dart and I'm pretty happy with it so far.
I adapted the air outlets from the new heater/A/C box to the factory under dash A/C vent box instead of using the Classic Auto Air supplied vents.
I blows really cold at around 40 DEGF or 5 DEGC.
It's nice that there was no cutting, drilling or modification of the firewall or rad support and you retain the factory heater control panel.