Many thanks to those of you who suggested Keith Kearcher to my younger brother. His Greener G60 (he found the grade marking not on the trigger guard but on the fore end iron) just back today from having had his barrels refinished, sighting ivory bead replaced, ebony diamond insterts restored, stock glass bedded and action tightened up. Keith measured the minumum bore wall thickness at .035. I think this one will be a good shooter for many years to come.
I'll leave it to my brother to post more photos, here is a photo of his damascus. Keith turned the gun around in record time (under 4 weeks). I think these barrels are the highly prized three iron. My brother just got the Greener book and wonders if these are the silver, stub, or other version of Greener's damascus.
