When the pulley comes off fairly easily ,I've removed the engine with the pulley on, then turned the engine upside down and held the engine off the ground by the pulley while the original pulley bolt is removed and putting a longer bolt into the end of the crank you hammer the bolt ,it's easier with 2 people.
Sometimes the hole in the frame won't allow the engine to be removed without first removing the pulley, then I have put wood on 2 spots opposite ends on the top of the pulley and with 2 long Tyre irons to lever the pulley down ,I will hit the crank up but is more of a tap with the hammer so as you are levering down you hit a long bolt in the crank upward and it will slowly move the pulley off but both these ways I will first use a lot of WD40 to soak in.These 2 ways are if it's not too stuck.
If you have to use heat you may need to replace the lower oil seal afterwards.
And below are a few other ways I would use if the pulley is really stuck.
