Some of the stampings on the heads could be from a rebuilder. I also think that some of them may be from original assembly at the Tonowanda plant, but I really don't know.
The heads appear to have been rebuilt once, or at least shaved once. The block is still standard bore, and doesn't appear to have been redone ever.
I'd be surprised if an engine rebuilder would put that many stamps on each head on a rebuild.
I'm trying to trace the history of the engine to determine how much has been done to it.
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Rick
69 Chevelle SS396 Silver L78 M21 Post Sedan (Berger Chev.)
69 Chevelle SS396 Black L78 4-speed 4.10 Post Sedan
Don't text and drive.
Somebody's life may depend on it!