Slant 6 Head Gasket Question

How's about personal experience? When younger and dumber, I compared the new gasket to my slant six head & block and decided one coolant passage should not be blocked by the gasket (probably the port you question). No internet then (we are so spoiled now), so ASSumed it needed a hole there and made one. Started the engine and after ~5 min idling it "seemed hot", checked the dash gage and it was pegged. Since everything was new, I was able to lift the head up 2" w/ the manifolds on and slide a new, unmolested gasket in and all was well. Best guess is that "port" is a "core hole" so the factory could shake the sand out, and was never intended to flow in any engine. Did I mention I had an M.S. in Mechanical Engineering at that time? Real-world experience is better.

Did you check the water pump? Mine has a sheet-metal blade that could corrode away. I verified mine using a $15 USB "endoscope" from ebay.