The restoration is remarkable, but the concept used in this construction is astonishing and innovative. Brilliant really, Walter Christie was a gifted engineer, and made the first front wheel drive car, http://justacarguy.blogspot.com/2011/03/first-front-wheel-drive-car-1904.html and raced it in 1905 in the Vanderbilt Cup. But getting back to the steam pumper... Christie didn't get in over his head and make the existing tech obsolete, he made it better. You may have realized that Microsoft is the world's top software company because it makes it's Windows better, not obsolete, and this made Bill Gates the world's richest man... improvements, not obsolescence.
Like I was saying, Walter looked at what needed to be improved, and took the opportunity to make horse drawn fire steam pumpers self propelled once they were equipped with his front wheel drive units instead of horses. Horses were already 10 years into the age of the car, and the writing was on the wall.
Fire department equipment is really expensive, and Walter focused on the biggest fire departments on the East Coast to contract with to improve the existing equipment to speed up the delivery of equipment to fires. Notice in the below photo that the front and back have little in common
To easily compare this to the horse drawn model, just click on this link and see it from my gallery http://justacarguy.blogspot.com/2011/03/san-diego-firehouse-museum_11.html last month of the steam pumper in the San Diego Fire House Museum: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhT2NFlRskCySidlDrK3t1bZSMn2bkXNLTWyhw9PB0Tq_IDMRAHGLPELQBF9OGyGfAgsloQJm_1umYimsz5ujzvrOkd-835l7tp6mBUNB6DsBNcu4mX1EOMdIAgLH6LYdIR3fY4sREfmRbb/s1600/DSC_0055.JPG 
This is just a short gallery, for a better one, and a full write up on the Christie company and it's founder: http://justacargal-s.blogspot.com/2011/03/1913-christie-fire-engine.html