My plan of action is to finish the Barracuda suspension side job in the garage (racecar financing). Then air up the cylinder and see if that pressurizes the coolant system. If not pull the intake and pressurize the coolant system and see if either of the
# 6 ports gets wet. Check lash, then pull the head and inspect. Measure deck height on #6. Tempted to pull the piston/rod even if the gasket or head is the issue. It doesn't a[[ear to have water in the oil. Never had any issue with Cometic gaskets, even after reuse ( these were new 91 passes ago). My bet is that it is the head. But we'll see.
Doug