The piston diameter, weight, compression height, and wrist pin diameter are all the same, so the 307 is a direct swap with no modifications necessary. I discovered that about 20 years ago when I was ordering parts for a student's 250 engine rebuild. He had a lead foot, and those 307 pistons turned his little 2-door Nova into a real hotrod!
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!