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Top pulley has to be pulled off , or pried up off the shaft, then woodruff key is removed, then the shaft can be driven out the bottom. You have the top nut off, and pulley is stuck? Use two pry bars under pulley and it should come off.
Works best with impact wrench, Or you will need to put the lower nut and blade back on the shaft to hold it.
I keep an electric impact for tires, to loosen this type nut.