I seem to recall reading that Chessie yellow on new EMD locomotives in the late 70's was just a Pantone hue or two away from the Federal Yellow that DuPont was supplying to the bus body companies (Bluebird, Thomas, et al). If you have a **clean** Chessie loco or covered hopper, try to ballpark your paint to that. Can't remember the exact source, probably in the Chessie locomotives book, or possibly on the hosam website.