I appreciate the response. I'm not sure I buy that though. If we were to believe that the engineers at chevy designed everything to the utmost of it's performance then we would never have to modify anything. We all know that's not true. I honestly just think about things too much and don't mean any disrespect by my thoughts. I just like to know the how and why behind the things we do and how my engine works.
What would cause the overheating if the passages were enlarged? It would seem that opening up the holes would allow better circulation. That in turn suggests to me a cooler running head. Maybe too cool. Maybe that's the reason or maybe not. Is it to allow air out when the water runs? Does water ever go through the upper portions of the head? I don't know, but I'd like to.