Except that there is no sign of the copper where the bearing rides only the exterior surface. That lends credence to the use of copper plating as an inhibitor of the carburizing process so that only the bearing area gets hardened.
I reconditioned hundreds of rods in my 10 years as a machinist. I have personally honed the big ends of many rods where the bearing surface had copper all over it. I've pressed factory pistons off of rods and found the honed pin bores with copper in them.
