Some are a some aren't. It will depend on the two years and models involved. A '72 Dart, Valliant, Duster Swinger, Etc are all the same. The '71's are not....there are 3 different ones that year. The 340's had one dash, the non-340 Valiant/Duster/Scamp had another, and the non-340 Dart/Demon/Swinger had a 3rd. What exact vehicles are involved in the swap?
The receiving car is a 70 duster. I believe the donor to be a 72 dart. both are a/c cars. I have a lead on two dart sports that I may be able to get everything from. Im reasonably sure that the dash parts i need will fit.
I just noticed that you said both cars were A/C cars. A/C and non-A/C heater suitcases don't interchange. The firewall and operating controls are different. If you want to convert it to non-A/C, I think I'd still use the A/C heater suitcase and just not mount or hook up the stuff under the hood. Cap off the unused connections in case you (or next owner) decides to get the system working again.