What parts are worth keeping off of a /6

There was a guy here that was quite insistent that he HAD TO HAVE Specifically a 1971 engine for some crazy reason. That's a 1971 engine. We keep telling him that they were all the exact same for so many years and a /6 powered car isn't critical to be " numbers matching"... See if he wants it. Other than that if it has a big "BH" cast in the driver side of the block there's something "special" about those, more nickel or something... Supposed to be the "strongest" block or something... I don't remember exactly what it was about them. Definitely a forged crank engine...