There are a few things you should consider. I highly doubt any GM dealer would have made a modification to the hood like that. Of most concern to me would
be the rain coming right in on top of the engine. With the car moving forward and the radiator fan going full out, the water pouring into those holes would be
converted into spray and subsequently totally soak the distributor, coil, and any other electrical connections against the firewall. Additionally, the idea of cold water
( in a rain storm ) continually coming down on hot cast iron gives me the heebee-jeebees. Chevrolet would have had a bird over these issues.........
And yes, JohnZ is correct - GM didn't design an open SS hood like this. Oddly enough though, I believe there was a louvered hood RPO that was cancelled in 1969.
Perhaps the engineers were trying to perfect a ram style louvered SS hood, but with rear facing openings that would be pointless.