dash and heater interchange

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.