As I tried to make clear above, I actually do have one. and I do agree that the parts are interchangeable. And because I could not find an RB dealer who has the K9 conrod in stock, I purchased a JL con-rod. It may fit but it looks nothing like the K9 rod that's in my engine. The JL rod had at least two visible cavities around the lower bushing area. Not the RB.
While viewing other replacement parts from the JL I noticed the differences that I mentioned in my previous post. But also notice the JL has a coated crankcase, and the heat sink is cut totally different. I would venture to say that the RB one weighs less and runs cooler, since it's drilled out. In fact I wonder if the entire engine is lighter than the JL, considering the aluminum wrist pin and pinch bolt.
Coatings can make a difference in performance, by for instance in changing the rate of a substrate's expansion from different temperature exposures. In other words it insulates. Remember RB started this for the old WS7 10 or 12 years ago. Also an anodized coating can allow a lighter-weight material to be used in place of traditional heavy material.
Who knows (yet) which mill will have the longer life. It will be fun finding out, but my money is on the RB.