Well I hate to inform you I had several 67 belvedere and Coronets I stripped with 318 solid lifter motors All my 62 - 66's had poly 318's . I first came across one in my father in laws 67 belvedere. I was changing his valve cover gaskets. And yes it was a 318 I looked. I adjusted his valves for the first time since he bought it.
I was his Hero, It was never that smooth and quiet. That is when he left me marry his daughter.
Poly rockers are totally different engines and only 2 valve cover bolts. I may have seen one or two in my 70 years. LOL