Ok as Tony was asking about fitting dcc in an electric Lew here are some photos of how I did it the easy way in my Countess. If Lew has a similar arrangement then it might be possible to copy this.
The limiting factor will be if the decoder will fit inside the boiler.
I built a sled from plastic, a flat plate with holes to allow the decoder to be cable tied to it and it has sides to insulate the decoder if it moves around.
The speaker is glued to the front end of the sled and sits in the smokebox. To stop any vibration I covered the sled and around the speaker with felt.
The wiring is coiled up so the sled can be pulled right out unplugged and swapped to my 7/8ths locos
All I had to do to rewire it was snip the two wires going to the motor, that pass up by the driveshaft. Extend these to a four pin socket with about 9-12 inches of wire, now do the same for the pickup side of the two wires you cut.
You should now have all four ends extended to the socket and this can be poked up through the hole in the boiler ready for attaching to the decoder. Just finally make sure the wires aren`t foul of the driveshaft, use a dab of silicon or epoxy if needs be.
