You can try using two large screwdrivers. Put the screwdrivers behind the pulley on opposite sides and carefully pry. Put the force, or leverage point, against the engine so the screwdrivers pry out as close to the center of the pulley as possible (if you put the force against the outer edges of the pulley you could bend it). Pry carefully with equal force on both screwdrivers. Also use some penetrating lube like WD-40. If it still doesn't come off you can put a bolt in the end of the crank and have somebody else tap on it while you're prying with the screwdrivers. And if none of that works, heat, and lots of it, is your best friend, but it'll probably ruin the output shaft seal.
