From the photograph, they don't look to be the original name and number plates from the loco.
Do you know what they are made of? The originals were cast at Swindon Works, but I'm not sure what the base metal was. Many years ago, I used to have a contact who could provide replicas, but these weren't worth anywhere near what the originals were / are (although they did cost a few quid!).
So, the key seems to me to be what they are made of - if you can say, this will help.
