R6 440 block?

Anyone know of a 1971 440 R6 racing block? Got a local guy trying to sell one complete with only 43k on it. Say's it was a very rare factory option racing block. I can't find anything on it except maybe they do make a modern nascar R6 block but he is saying his is a factory 1971 engine that he pulled out of a barn find.
Waiting for him to get me vin and casting codes.