This is Revell's second steam engine offering and is first found in the 1959-60 catalog.  The 0-4-0 Yard Hog Switcher powers a pair of train sets in 1959 and is also listed as being available separately for $8.95.  Unlike the Revell 0-6-0 Steam Loco, the 0-4-0 did not produce smoke.  The Pennsy example is the only roadname Revell produced for this model.