(Click image for larger image)
Modeled after the Spokane, Portland and Seattle 700 4-8-4 Steam Engine. This engine, with it's tender is about 72 studs long and negotiates the curves like a champ. In fact, it's so massive, it will not tip over at full throttle (so far). The real 700 engine is currently housed at the Brooklyn Yard Roundhouse in Portland, Oregon and is one of only five 'Northern' Class steam engines still in operating condition in the United States.
Here is the tender. Note the wheels, two bogies with six wheels each. Much like the real thing. West coast steam engine tenders generally held water and fuel oil for the engine. Coal wasn't widely available in the Pacific Northwest. Thus the tender is basically a tank car with two large compartments. One for water and the other for fuel oil.
Another picture of the engine. Too bad the color scheme is mostly black, most of the details can not be seen in this picture.
A better view. Note, the boiler is five studs wide and I used a large technic hub for the front detail of the boiler. The front truck uses gray freestyle wheels with the outer flange machined off. Using these allowed more flexibility for building the steam piston and valve block immediately above.