Clem passed away several years ago. RIP. His wife and trainz partner, Linda, was answering email last year. Together they were bnsf50.
Linda's email to me said, in part,
"I will tell you the same as I have told others that want to update. You are more than welcome to do as many of the items that we put on the Trainz download pages that you want. My only request is that you give Clem credit for the original work.
Thank you for contacting us and asking for permission to do this."
I would suggest a credit to "Linda and Clem - bnsf50" would be appropriate.