You need a new vibration damper- - - -the outer ring and the rubber piece that holds them together is missing. There are new ones available on Ebay. The original damper for a 265 was 6" in diameter, but slightly larger ones will fit and work OK as long as the damper doesn't touch the motor mount brackets on either side of the crankshaft snout. Any 3-bolt Chevy pulley should fit, as long as it clears the motor mounts.
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!