Re: Motor locked up
Welcome. There is a lot of great advice here.
Yes, You should be able to spin the crank with the head off the engine.
I would avoid trying to turn the crank via the propeller. Can you get the flywheel back on and use it to apply torque?
There are a couple ways to go. You can try to unfreeze the pistons from the outside, not really ever intending to split the engine block or you can sign up for a block tear down.
Although not popular, I have been successful in the past inserting a wooden dowel into the spark plug hole and tapping the piston while applying torque to spin the crank. Not popular, but it has saved me a few tear downs. If you have the head off, you may tap the pistons with a wooden or plastic mallet; tap not bang The pistons rings and / or bearings are frozen. Can you get anything like PB Blaster behind the piston into the crankshaft bearings? Maybe you can snake one of those red spray straws behind the pistons. Do you have the inspection plate and exhaust plate off?
There may be a lot of torque required to break the crank free. I wouldn't recommend trying to get that much from the prop.
J