Greg,
An excellent source for this type of info is the Yahoo groups Critterslist, which caters to industrial rail lines and equipment. I've asked a lot of questions there and someone always seems to have the answers. The URL is included below, but I'm not sure if the list is set for public input or if you have to be a list member to post. If the latter, let me know, I'll be glad to pose the question for you.
Jeff