Off topic but , Paul, do you have a link to any photos of your railway. I'm really admiring the attention to detail that you have.Greg,
With the Airwire G3 and the newer G4 decoder if you don't know the address or the frequency you can set the transmitter to the default of frequency 0 and address 3. Then turn on the loco and wait one minute. The decoder will temporarily set itself to frequency 0 and address 3. At that point it should work and it can be set to whatever you want. Kind of a brief explanation, there can be a little more to it, but that is basically how to recover a decoder where the frequency and or address is unknown. If a decoder is turned on and it doesn't see its frequency in one minute it goes to default.