Confused about block casting number

[Kw69]

Hey guys,

Ok hopefull to gain some understanding here on my truck engine. It's a 69 and has the casting of that year of 3956618. In the past my research stated that it was used for 1 year only and only cast for a few months. It's the same block casting of the 302, 327 or 350 of the 69 engines. So again forgive me I'm just trying to understand because I ran into a guy today that had a 302 1969 z28 with the same casting number. So in speaking with him, I was told that this was a rarer block because of the casting and had a high nickel content. I know the internals were different with the 302,327 and 350, but was anything different about the bare block itself? His is a DZ designation and of course mine is not being a general 350 and not a 302. Again forgive me I just don't know, at 44 I'm always learning and enjoy doing so. I p,an to rebuild this engine in the spring and reinstall it back into the truck and use the current crate 350 in another upcoming project. Thanks