You will have fun with this seal change project... Start by pulling off your governor and its attachments, your water pump, and generator to clear the area, then get a torch with map gas and heat up the nut until it is good and hot, then get a 5/8 inch brass punch and knock the nut counter clockwise to loosen it or a pipe wrench if it still doesnt want to move. Then heat the pulley hub again with the torch and use 2 flat pieces of rigid thin metal like tapered pry bars that are about 2 inches wide and carefully and evenly pry off the pulley from opposite sides. Dont worry if the seal catches fire or smokes; just blow it out. You will then need to remove the forward engine support by jacking up the forward end of the block by the pan with wood placed to spread the load so you don't dent the pan. Don't loose or confuse the shims under the support on each side. Also don't jack the engine very high, just enough to relieve the load. The seal has to be replaced by removing the timing cover and trying to drive the seal inward around a metal flange and through a felt dirt seal all driven in the backward direction toward the block to remove. You could also use an expandable seal puller from the back side of the timing cover and knock it back out. Then install the new seal from the back with the correct orientation with flat face of the seal on the forward side. To do so you need a tool that fits the thin side edges on the back side of the seal and carefully drive it so it wont be ruined. You may need to take it to an expert here if you don't have a good tool. If you are really good, you might be able to remove the flange that is blocking your way in the seal hole. This would allow you to install the seal normally from the outside face. To finish, clean off and replace the timing cover gasket and put the thing back together in reverse order. Good Luck!

I got the nut off one with a pipe wrench.  It wasn't easy, though.  The pulley slipped off but the front seal is pressed in from the inside of the front cover.  I didn't want to get into that job at the time.  You could try repairing it with a Speedy Sleeve from CR Seals.  It's s thin stainless steel sleeve that fits on the pulley shank with a little Locktite.  It makes the shank a little larger and gives it a new smooth surface for the seal.  You can get one from a local bearing supplier.  Cost a little over $20.  I used one on mine but it didn't help much because the crank was too loose.