The big nut contain the bearings that are held into the nuts with snap rings. They unscrew RH thread.There are also snap ring on the shaft out side the nuts. Best way is to get the rear nut unscrewed and off the shaft, then unscrew the front nut and the assemble should come out the front of the tractor. Than you can get it in a press to complete disassembly. There is a snap ring on the shaft behind the front nut that keep the shaft from floating forward with in use.
You may get lucky and find a pulley from someone or on ebay if not i believe i paid close to $85 for the pulley plus shipping which put it close to around $100 just for the pulley i bought through partstree someone should have warned you about that pulley on putting some panther pee on it and letting it soak for a day or so and maybe some heat beforehand I did the same thing once and it was an expensive lesson