The code is finished to a feature complete state so I have installed the whole system in my Suzuki Jimny.
The Cobra CB is installed where the ash tray was and looks really tidy tucked away down low. You can be listening to music on one of the other sources and when the squelch is opened by a signal the head unit will make the CB the active source switching over to it and showing the channel, frequency and RSSI. When the squelch closes it returns to the original music source. If the source was Bluetooth or USB playback it will be paused and will resume where it left off.
Testing so far is positive with it all working as I hope at the start of the project.