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I'm not familiar with the cooling system design on a 327 when used in a boat, but if the thermostat is at the high point of the water, then I can't see how it would not trap air under it until it opened. If it's a closed system that recirculates, once the thermostat opens the first time there would be no more trapped air, but more coolant would need to be added. After that there would be no issue.
When filling a closed system for the first time, any dead end at the top will certainly trap air and prevent the water from reaching the thermostat (if it's at the highest point). Drilling a couple small holes in the thermostat lets the air escape. Doing that will not noticeably change the warm-up time of the engine (the flow rate is minor through the holes) but it may save the engine from overheating if the thermostat is trying to operate on hot air rather than hot water.
Again, I am relating automotive experience.