i think they are pressed on,
I would take it to a shop and have them press it off, sometimes even with your best effort, you destroy the pulley or pump.
be sure to measure the distance to the pulley from the base of pump,
so you can press it back to the same place or if you are moving the location of the pulley, you will need to know the correct distance or location as it will have to be press on to that location.
Just my two cents,
the last water pump i had replaced on my TO-35 the guys were very careful and had heavy duty press equipment.
they were ale to press the pulley off the old pump and press it onto the new pump without damage.