Re: copper plated connecting rod?
No mystery, if you have ever worked in the motorcycle industry. A friend of mine has, for years, and what is done with the copper is done to localize heat treatment levels.
"Motorcycle full circle rods don't have any parting lines in them on their big ends, and use roller bearings, no bolted on caps. The rod would need a different heat treat on the load surfaces on either end, bearing hardness, and a completely different 'softer' hardness treat for the beam section. The copper draws heat away from the base metal it is clad to, and the treat is lower than unclad metal areas. So, the rod gets treated bearing hardness on the inner race ends, and a completely different hardness for the beam and outer ends. Bearing hardness treat for the beams would make the beam much more brittle, and subject to cracking/failure/breakage. I understand new rods in selected automotive engines, especially General Motors U.S. manufactured engines, go through this dual, or multiple heat treat process, especially if they are cast, and some forged performance rods get it too, to assist in the stability of the bolt boss, and other areas of those rods."
Hope this helps.