[Steve Shauger]

Lets be respectful to one and other. It's a slippery slope when a theory is purported as fact. I don't want to squelch debate, but facts need to be introduced to support them or mis-information turns into myth and later fact.

I do believe the casting #'s represent running changes for strengthening, manufacturability and various improvements, which are documented with examples. Regarding block material being identified by casting identifiers... well this is completely unproven. We have two notable authorities (John Z. & Bergy) who have firsthand intimate knowledge and have debunked the nickel and tin content variants based on application theories as it relates to Chevrolet built engines.