It's not uncommon to find grinding marks on weight-matched rods. The rebuilder uses a fixture to hang the rod by the small end and weight the big one on a triple-beam scale or a digital one. Then the rods are weight-matched to the lightest one, and they're swapped end for end and the small ends get the same treatment. Most inline six crankshafts are very close to properly dynamic balanced, but some shops spin the crank without bob weights and do a final tweak to eliminate any vibration. It sounds like somebody has gone to a lot of effort to do a very good buildup job. I weight-matched rods on the race engines to a tolerance of 1/10 gram. A dollar bill weighs one gram.

I usually like to rotate a lip seal a little so the parting lines of the seal and the block/cap junction aren't at the same place. Best Gasket rope seals are intentionally over length, and must be trimmed to fit. Don't try that on a lip seal!
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!