Generally, the numbers are placed on the silver body panel centered under the black window band. An article in the May 1995 issue of "Railroad Model Craftsman" and the following photos might help.
http://railpictures.net/viewphoto.php?id=158077
http://railpictures.net/viewphoto.php?id=136058
http://railpictures.net/viewphoto.php?id=135371
http://railpictures.net/viewphoto.php?id=130711
Bill
"Never try to teach a pig to sing. It wastes your time and annoys the pig"