I have a set of chrome valave covers that came off my 67 firebird 400 back around 1992. As far as I know they were the original covers, but how can I tell? They are heave gauge metal, but have no GM part number anywhere on them. I am in the process of figuring out whether to re-chrome these or buy re-pops if these turn out not to be the originals. Any hints and ideas on how to tell?

These are off of a 67 400 that has the oil drippers in the head, and not in the valve cover.

Thanks!!