Big block 440 in 71’ Dart “Heater box does not fit”

the firewall for a/c and non a/c cars have different openings.
Of course it would……. I wouldn’t want it to be easy. I’ll have to find a non A/C Dart to see the difference. Looks like I will be searching for an A/C heater box…… Thanks for the info. Better to find out now.