This was my very first loco, purchased a good 5 years before I had track to run it on! The plan was "when a DCC decoder goes in this, they'll go in anything".
I've recently re-done the decoder installation. First time around I isolated the pickup strips using Kapton tape. That seemed simple and worked, but it also created play in the wheel axles, and the engine ran erratically. I've redone the installation using the DCC Supplies"DiGiHat" plastic bush to isolate the bottom motor brush: this is simple the pickups are now connected back to the chassis. the DZ123 fits into the back of the cab: I had to remove its red heat-shrink and re-insulate with Kapton tape.
For those interested, the decoder installation is now essentially identical to that for the class 08 shunter.