Fairly certain that the loco has the Kato-made version of the mechanism as described here: http://www.spookshow.net/cce78.html If so, you can send the metal frame out to Aztec for milling to create space for a DCC decoder as shown here: http://n-scale-dcc.blogspot.com/2014/01/tcs-m1-in-older-concor-e8a.html http://www.aztectrains.com/dccframes.html If that task is more than you want to tackle, it's possible to have someone else do the job for you: http://www.aztectrains.com/dccinstallers.html
You would have to mill a pocket in the frame to hold a hard wired decoder. I have done a few in the past. Or put the decoder in the dummy unit and run the decoder wires through the port holes on the end doors with the locomotives MUed together.
CON-COR says the motor needs isolating also. I want to push my luck and put a sound decoder in so I am going to need space to the speaker too. Ok yes! I want it all....
