Marine 273 build

Im reading a little more and it looks like 273 marine heads that I keep calling "318 heads" were actually offered on both the 273 and 318. My buddy's boat had 675 castings. (This would make sense since the 675's look to have been installed in later 273's. The marine industry lagged the automotive by a year or 2 back then... our boats with these 273's were generally built '67-72). Is this head chart correct?

http://www.mopar1.us/Aengine.html

If so, then it looks like there is only a 3cc difference between the earlier 273 heads (57cc) and the 675's (60cc). Im reading on here that the 302 heads are ~64cc... so that would be going in the wrong direction, no?

Anybody have a good recommendation on a set of heads that would boost compression into the mid 9's? Swapping pistons isnt on the table (for me) at this time... though my buddy with his egge 10.5:1 pistons is looking smarter and smarter. If my math is correct, I'd need to get down to ~51cc chambers to get 9.5:1. Does such a head exist?