308 vs. x heads

I know a guy who did a lot of testing in the early 90s with x and 308 heads ported unported small valves big valves everything his conclusion was unported 308 with 2.02 valves was a 40 hp gain over the x and ported done right was more but he said the intake port is ticklish and can loose velocity if done wrong. I got a ported set of 308s from him in the early 90s and liked them well. what I know is what I was told if it means anything.