There is virtually no overlap on a stock stovebolt cam. Watch the rocker arms sometime on a valve adjustment. The exhaust valve closes before the intake rocker even begins to move. That's the main advantage of the 261/Corvette cam- - - - -much longer exhaust duration for better cylinder scavenging.
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!