Out here in western Washington State, a man named Gene Frase built a steam powered saw mill out of used pieces from other mills that were converting to electricity or some other form of propulsion back in the late 1950's. He ran his mill (single-handedly alot of the time) until 2009 when heavy winter snows finally collapsed the mill's roof and upset the foundation logs under the carriage. Before he passed, Mr. Frase generously donated the mill machinery to the Mt. Rainier Scenic Railroad for inclusion in the new Murray Logging Museum located in Mineral, WA (about 50 miles from the mill site). To see the mill in all its glory, check out this link:
From what I can see in the pictures, the carriage moves along fixed rollers, rather than the carriage having wheels and running on a bed track --but I know that there would be no lateral guidance if that were the case.
Hard to see in the pix--lots of atmospheric steam, but that doesn't help looking at details. Do you have a photo of the carriage in storage at the museum?