Air cleaner decals mean nothing.
My mom's best friend had a 69 Olds cutlass, bought new, with a 455 in it. I wanted that car, cause I knew there were no 455s in cutlass/442 till 70.
A few years ago, it needed some engine work (head gaskets if I remember right) and strangely enough, 455 parts didn't work.
It was a 350.
I also remember a guy racing a 70 Montecarlo at the original Irwindale raceway, with a LS6 in it. He claimed it was a factory Copo car.