There are more of us Wild Mary fans out there than you might think and if you are willing to do some research, there is a fair amount of written and visual information available to help you.
My particular area of modeling emphasis is late steam/early diesel ( includes Challengers, Potomacs, Decapods, Consolidations, and Pacifics on the steam side and RS-3's, GP-9's, BL-2, F-7's, and FA's on the diesel side). By definition I stick to Fireballs or Speed Lettering -- no circus coloring for my motive power.
Both Knobmount/Ridgely and Hagerstown were classification yards. Watch out that you don't confuse the WM yards near Cumberland with the much larger B&O operation there.