how to id a big block?

[DSYenko]

Im no expert but a 512 block can be either a 454 or a 427.But with a "L" casting date im guessing 454.What would help is if you know the info stamped on the deck ahead of the drivers side head.

[Unreal]

427 is internally balanced, and 454 is externally balanced. If the balancer has a counterweight cast in the back side, it's a 454 balancer. Look for engine codes on the pad in front of the pass side head. Based on the cast date, if it's a CE, it could be either a 427 or 454. If it's a standard engine build date/application code, it would be a 454.