Tim, the NOS Nasco block I had was over 25 years ago now ( when no one wanted them ) and I still remember it had that waxy type protective coating you often see on NOS metal parts and the green was a sort of lightish industrial looking colour ( how do you describe a colour in words

).I guess it could be possible that it may have been unpainted originally and some previous owner had painted it the green colour that I found it in ...... dunno ??.
It was sitting in the rear of an FB wagon that was given to me at the time alomg with some other parts.
From memory it was unstamped and I spent a long time at the local GMH parts counter trying to find out details of it.Eventually the old shop foreman walked in ( he was an apprentice in 1948 when the FX's hit the showroom floor ) and he said it was a 138 replacement block.When measured,it had a standard bore and had definately had no use as indicated by the bores condition.
Dickhead me gave it away eventually

I can't think what to write here so this will do.