We are unsure if someone has done head gaskets on the car before or not. We did not dig that deep down as we were told it was a Intake Gasket problem.I've had issues like this, especially with heater cores not flowing. I find that used cars over time have been filled with well water, or something besides distilled water and have cloged passages from iron and other things in non pure water over time. I go to Walmart and get the 38 cent a gallon drinking water from the water dispenser and use redline water wetter (from autozone) and 20% antifreeze in summer, and 50% in winter (in Tennessee) always using the water wetter as it increases the heat transfer of water better than antifreeze. there are several other things I do with cooling, but I feel you have a clogged block or head passage somewhere after reading about everything you have done. I just wonder if someone had previously put head gaskets on this block?