A 327 has a 4" bore. That would be a .125" overbore, and you could read a newspaper through the cylinder walls. The 307 piston has the correct bore/compression height to be a direct replacement.
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!