My guess is that they will probably use the same bits they did with the last J's they ran. People such as myself wouldn't know the difference, but the scholarly people who know will. Either way, they will sell because of other new features like whistle steam this time around.
I myself didn't get a J the last time they offered them(a little late to the show) but I said to myself that they'd be back around. I went for 603 because of the doghouse. I also went with the cavalier cars because I actually have an old set of MTH N&W cars from way back when. I never did get the engine that went with it, but that's okay.