As probably the IW member with the most years of racing model outboards and a HOBBICO sponsored racer before Grim started working there, I find this discussion very interesting. I also have the somewhat unenviable record of being disqualified from 3 NAMBA National Outboard Championships because parts of the engine/s I was running were not stock. It's a lame excuse, but the parts were borrowed from other model boaters and I assumed they were stock. However, we all know about "ASSUME."
My experience with allowing the interchanging of parts between different engine generations as allowed in NAMBA has been basically, "What's the big deal?" I need to quantify that this observation has been made with K&B engines. I have not observed performance gains just switching parts. However, I have witnessed performance gains when making internal modifications to engines that compete in the IMPBA 20 Sport Tunnel Class. When I race my NAMBA legal O.S. 21 Outboard in Hobart, I accept the fact that I don't have as much power as some of the other contestants. I just accept the situation and enjoy the opportunity to compete at a very high level.
Since I don't have a horse in this race, I probably shouldn't be posting on the topic. However, I think my post is more of an observation than a position.
JD