Union Pacific 'Challenger' Production Details 

This late coal version #3 model shows that in later service the secondary air inlets were removed. You can see the folding footsteps prototypically located on various locations on the boiler jacket, you can also see the top center one is in the open position, they do operate. The access doors are also operational on the firepan, this photo shows two of the doors open, they are held closed with functional latches. At the top right, you can see the 'Clear View' front cab window which has a pane that actually opens.