This was when the Rock had a piggyback yard all the way downtown at the south edge of the Loop next to the LaSalle Street Station Leads. Baldwin Locomotive Works made 63 S-8s (54 A-units and 9 B-units) between 1950 and 1954. I don't even remember seeing a picture of a B-unit but Google found pictures! http://baldwindiesels.railfan.net/oim/index.html