In 2012 the NNGC will start off with a ride on the Mt. Rainier Scenic Railroad.
This excursion is scheduled to be an all day trip including several runbys staged for the convention attendees.
Currenlty Mt. Rainier Scenic Railroad operates a Heisler (one of my favorite steam locomotives), a Climax and a 2-8-2T. I'm not sure what the train at the excursion will use. Hopefully it'll be a smoke bellowing, steam chuffing beast.