Chuck, Carl did a one -off conversion of my FlyerChief Northern to TMCC/Railsounds. I do not think it is documented on his website. I feel it was worth the cost to get much better operation on my layout using the Legacy control system. If you look on his website at the conversion he did with the FlyerChief Berkshire the result is the same but there were some challenges unique to the Northern in completing the conversion.
I, myself, did a conversion of my conventional Flyonel Northern to TMCC. I was fortunate enough that I had a Cruise lite board and an ERR Sound Converter. I found enough room to do the conversion and still use the Railsounds that came in the tender. I need to look at the fan driven smoke unit.