You could have stuck valves too. Look closely at each plug as you take them out the one with rust on it will tell you what cylinder had standing water. The old 216's had cast iron pistons that some times stick to the cylinder walls also. You can loosen the valves with wd40 or like oils. When you do try to turn the engine over leave the plugs out incase of any standing water or solvent in the cylinders. All good things come in time and it may take plenty

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