A little closer look tells me this was based on the army mobile forge. Right bellows, for one thing, and the positioning of the forge proper. Because it was used at the LA Fair, there wasn't a need for the coal bin that is at the back of the wagon. The tool drawer back there uses the space that was used for steel and iron storage in the originals (the tools were stored in the "limber" cart that pulled the forge).
This is way cool!