Okay, I hope this helps. I know that Crower manufactured an experimental 4 valve head for small-block chevy's in 1965 and Chevy engineers looked at that possibility. But, there is a company out there that makes them now. I read an article a couple of years ago in either Hot Rod or Super Chevy about a small company that was making quad valve cylinder heads for small-blocks that were run off of the original cam. If you contact customer service at these publications they will send you the info that you need to get these heads. If I remember right these heads were expensive, but man-o-man did they get power.