[hamjet]

I haven't checked, just shooting from the hip from what I remember. 1971 was the first year they started dropping compression. they probably played with lift and duration to coincide with the drop.Open port heads, (we used to call them rectangle port) were for the 375 HP and up 396/402s. more compression, if you mean larger combustion chamber, I don't know for a fact if they dished the pistons, opened the combustion chamber, or both when they lowered the compression in 71.