I'm not sure of the state of the M1b. We never made it to the yard as we had guests and hungry kids. They were trying to raise $250K to restore 5 steam locomotives, M1b and K4 and a few others that will eventually be stored in a future roundhouse... not sure if the roundhouse was every built or not. If $250K is all they think they need to restore some grandeur to 5 big locomotives this doesn't sound like anything major needs to be done or if it's just body work and paint.
I volunteer at the museum, and the money being raised is to do just what you said: to get 5 steam locomotives (M1b, K4, B6, H8 and L1s) stabilized and cosmetically restored to be displayed in the new Roundhouse, which is now slated to have a groundbreaking next Spring (hopefully!)
The E6 which was just restored recently will be the centerpiece, set on a rolling platform to move the drivers, with the other 5 displayed out from that in almost a turntable setup.
I believe the B6 is now in the Restoration Shop or will be soon, to get her started.
The folks there have recognized for a while how much those 5 engines, as well as many others in the yard, need some work to defend against the elements. Budget concerns pushed a lot of the projects back, and from what I'm hearing, after the 5 steam engines are ready, next up is 4800, to be restored to the "as delivered" scheme.
Glad you enjoyed the museum! I ended up volunteering because I'm there so much anyway!