[Another Bolt Removal Tip from Don Foster: The Rope Trick] Use nylon rope to jam the piston at TDC while you turn the crank pulley bolt. Be careful how you do this: you can damage the valves.

Be absolutely certain you're at cylinder #1 TDC between the compression and power strokes. This way the valves will be closed. You can tell this by feeling compression pressure, using your finger, in the spark plug hole.
Turn the crankshaft clockwise (facing the engine) about 1/4 to 1/3 turn. Stuff in about 2-3' of 1/4" soft rope — nylon or cotton clothesline should work.
Turn the crank counter clockwise as to unscrew the pulley bolt. The rope compresses and jams the piston. Using a breaker bar, loosen and remove the bolt.
To reassemble, use the same approach except stage the crankshaft about 1/4 to 1/3 turn counter clockwise from #1 TDC. Stuff in the rope. Turn the crank clockwise to compress the rope and jam the piston. Tighten and torque the center bolt following the "torque and turn" procedure.
Remove the rope, install the plug.