Well if it were mine, I'd drive on the piston with an oaken block and have a helper try turning the flywheel @ the same time with a pinch bar in the teeth, or @ least hold tension on it trying to turn in the right direction.
do clean up the bore with a deglazing hone somewhat, because when one piston it going down the other is usually coming up depending on the crank throws.
Also use plenty of penetrating oil.
once it moves ever so little, reverse direction working it back/forth.
