I am not positive on the black versus the plating for each specific years on B bodies and I would naturally research it before shipping your motor back.
I do know that I have several 70 motors that were clear zinc plated.
Charles i would definitely test the motor before shipping and correct all problems before doing so.
I left you a phone message.
I have never seen any gold plated versions.
Best way to check that out would be to open it up and see the plating inside.
By the way the photo above is of an e body. They were all clear zinc plated.
thanks
Jules