This is a fun mystery. I would like to see also!
Mostly I would think that the partial VIN# on the passenger side oil rail boss would tell most of the story.
If I ASSUME correctly that it's a '72 engine, there's only a handful of cars it could be, right?
Like Challenger, Barracuda, Charger, Road Runner, Dart, Duster?
They didn't put 340s in everything, or did they?
Awww...nevermind, I give up....
Check the drivers side front boss stamp again for more #s as that will reveal the plant it came from.