This locomotive got the "Malley" part of her "Valley Malley" name because she was originally built as a Vaulain compound locomotive. (Baldwin, 1901) "Malleys" are ordinary articulated locomotives with 4 cylinders -- the rear 2 are are the 2 high-pressure cylinders, and the front 2 are the 2 low-pressure cylinders. ("Malley" is the pronunciation of "Mallet": the last name of the man who invented this system, the Swiss engineer Anatole Mallet (1837–1919).)

Vauclain compounds have 4 power cylinders, 2 on each side, with one cylinder on top of the other cylinder on each side, looking like huge steam chests. The photos I have seen of the Manitou & Pikes Peak Railway #4, which is a Vauclain compound, show her as having 2 cylindrical shapes on each side, with the one on top being wider than the one on the bottom! When I first saw photos of her, I thought it was really odd that her steam chests were wider than her power cylinders, but what I had thought were her steam chests were really her other 2 power cylinders, and Googling showed me she was a rare Vauclain compound. She is, according to Wikipedia, the only operable Vaulain compound in existence.

Here is some info about Vauclain compounds:

https://en.wikipedia.org/wiki/Vauclain_compound

Here is a photo of the Manitou & Pike's Peak Railway #4, which shows her with her odd-looking Vauclain compound cylinders, with no articulation, and with the wider low-pressure cylinder on top of the narrower high-pressure cylinder:

http://www.flickriver.com/photos/midasmulligan/8365997533/

Back to the SP 1744. The SP 1744 was "simpled" -- converted to conventional 2-cylinder operation -- in 1912 and 1914, and was at that time converted from burning coal to burning oil. She is a "Mogul" -- a 2-6-0. I learned the SP 1744's history from the one reply to a question back in 2007 about her in this short discussion about her in the Trains Magazine Steam & Preservation Forum:

http://cs.trains.com/trn/f/740/t/99934.aspx