I have no idea if this is still in print, but in 1980, Guy Dunscomb and Fred Stindt collaborated on a book called WESTERN PACIFIC STEAM LOOMOTIVES, PASSENGER TRAINS AND CARS that is exhaustively detailed with photographs and information on almost every steam locomotive the WP ever ran. The book was privately printed by Mr. Dunscomb in Modesto, CA. The address is given as: 2502 Fremont Ave, Modesto, CA 95350. The Library of Congress card is No. 80-50321
I hope this helps.