NG critter question

I was about to head out the door this morning to spend the day working on "stuff" at SVRy, when the ph. rang and as a result ended up spending the day on a service call. As a treatment for rr withdrawl syndrome, this evening I cleaned up the nameplate for our ancient non operable Plymouth engine. The nameplate was nearly illegible and had quite a bit of damage, but I was able with a little elbow grease to clean it to the point where I could read the entire thing. It says: Plymouth Gasoline Locomotive
#2533 Type 4 Model HL
Ga.36 Wt. 20ton
The Fate Root Heath Co
Plymouth Locomotive Works
Plymouth, Ohio, USA
Does anyone know the history of this engine? I know of course that we got it from a creosote treat plant up Puget Sound way that was an EPA superfund site, but I suspect it has some history long before that. It has a similar Climax engine to SVRy 100. Any idea of the age of this engine? Was it built with the lowered cab, or was this a midlife addition? It is propane fueled, but again this may have been a modification that occured long after it left the factory?