Sorry, I have a passion for those old steam-powered logging machines, and feel compelled to clear things up a bit.
The model on the flat car (which is very nice, I might add) is a "steam donkey" or "donkey engine". Such engines could be used for a variety of tasks, including yarding, roading, and loading. They could also end up as the power for slide-jammers, McGiffert and Decker loaders, pile-drivers, etc.
Technically, a "skidder" is a large logging machine that combines two or more steam donkeys on one frame (usually either a wooden sled or a railroad car). One engine would be used for yarding, another for loading, possibly another for rigging the whole setup. The largest skidders would be moved from place to place on two flatcars, had multiple donkey engines, a giant boiler, and a 100 foot steel spar sticking out of the top.
Steam donkey :
http://content.lib.washington.edu/cdm4/item_viewer.php?CISOROOT=/clarkkinsey&CISOPTR=1132&CISOBOX=1&REC=9
Skidder:
http://content.lib.washington.edu/cdm4/item_viewer.php?CISOROOT=/clarkkinsey&CISOPTR=618&CISOBOX=1&REC=17
All that being said, it is a very nice model. Have you considered replacing the factory skids with a log sled and "donkey house"?