Wiring/ecm/pcm/etc. interchangeability?

The short answer is yes, sort of.
The reality is you will find different harness connections, so they won't just plug in and work, but if you have both harnesses from both donor vehicles you can make it work by changing the connectors as needed.
The electrical version of the manual AC and heater controls are regular switches, so wiring those in to work is simple once you have wiring diagrams for both donors.
The real question is, what exactly are you trying to build? Is this going to be an A body with factory heater/AC case under the dash or are you trying to put a Ram or Dakota heater/AC case under the dash and mount the Dakota controls in the A body dash?