Have you checked the connecting rod for bend or twist? The machine shop that's advising you sounds like they might understand how flimsy stovebolt rods are. It's very easy to bend one while installing pistons, and a bent rod can cause all sorts or oddball wear patterns and noises.
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!