I'm going to be doing some comparison checking soon, mostly on the 216 head, but I believe I've got all the 235 and 261 heads on hand as well. I'll be glad to post the combustion chamber volumes I get for each one. The "true" compression ratio is also dependent on when the intake valve closes as the piston is on its way up the compression stroke. That's why camshaft manufacturers recommend high compression when an engine runs a radical cam- - - -there's less cylinder left to compress as the intake valve duration increases, so "high compression" is simply an effort to get the real compression pressure back to where it used to be with a stock cam.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!