[Mr70]

It looks like there was a 1 ground down after the 7,indicating a 1971 Casting date on this #854 block.
You said it has the enlarged opening for the external Oil cooler,but I would like to know if it really does
indeed have 4 bolt mains by removing the oil pan.

My .02 opinion
The CON VIN pad stamping doesn't look bad,but is questionable as well.It's not upside down either.
Someone possibly ground of the 1,possibly enlarged the External Oil cooler opening,and restamped
the pad to reflect the 1967 Chevelle-Elco L-78 vehicle it went into,made at the Kansas City Plant.
I feel it's a 1971 cast #854 block with two bolt mains originally.
I've yet to see one cast after 1970 that did.