Cool find. We found something similar on an LS6 engine block after it came out of the gunk tank. The first scribblings make no sense to me, but the second picture is pretty obvious.
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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!