I believe the OD is 6 3/4" but the belt grooves are machined into the balancer outer ring. I've seen several of them adapted to stovebolt engines.

www.ebay.com/itm/145926932748?

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!