1972 LS5 Chevelle date help

[Grim70]

I'm helping a friend of mine put his engine bay back to correct dated parts. The original engine was removed at some point and replaced with a 1975 454 in NE Wi in the 80's. He's owned the car about ten years.

The car is a KC 3rd week of December 1971 car (546,376). I found the build sheet for him recently.

Looking for opinions or similar examples where this block date and parts would've fell. I'm thinking if I find him parts in October to early November 71 we should be good?

Any input appreciated.