So mine arrived tonight and the answer is a 21pin DCC decoder for each end.
Wow, I thought the N class was Auscisions hardest to open loco. This one has simple clips like an old Lima model, but you will almost certainly leave gouges in the body doing it!
edit: An hour and a bit later I've got a lokpilot into one end!
I'd suggest having a lot of credit/store cards handy to hold the side clips apart and just accept there will be a lot of horrible sounding cracking noises! Start at the B end and work the cards forward along the join. It runs right under the doors and main side windows around floor level at the ends.
The instructions don't include it, but make sure you swap the lighting connectors from the DC to the DCC sockets on the main board. The DCC ones can be hard to spot under the wiring.