They rust on solid if not removed and greased from time to time.
If you can get to the keyway spray you favourite penetrating goo up from the bottom and down from the top.
Leave the bolt loose a few turns, put the deck back on , start the engine then continually flick the blades on & off.
If you are lucky the shock loading will free it up and it will fall off.
Keep the deck on the lowest setting so you are also getting some down pull.
Is the hole in the mounting plate big enough to remove the engine with the pulley on it ?
