Once again, persistence prevails. I know you’ve been fighting this for a long time now, so congrats on figuring it out and getting it to run properly. You can see the imprints of the 2 blocked holes on the gasket – good find. Not sure what other gasket would be interchanged on that model but I know the power head base gaskets on some mid 50s model can be similarly interchanged with the same overheating result.