I seen this engine inside a '69 Corvette running. The number of months later the Corvette owner remove the engine and put a 496 cubic inch and the Corvette.
I purchase the engine off of him and it has been sitting at my shop undercover ever since. Don't look going to use it anytime soon put it up for sale!
It's stamped high performance on each side of the engine. I don't know much about engines overall I don't think it's a rare engine but it is stamped high performance and I did see this engine run in the Corvette.