Drive pulley replacement help needed- rear axle pulley

I have an older model riding mower and the rear drive pulley needs to be replaced, I bought a new pulley and removed the retaining ring but the outer part of the pulley rusted off the shaft and came loose when I tried to see if it would just pull off, it didn't. There is a piece that is not square but close that looks like it needs to come off but I don't know how it comes off. The model is 917252500 and the diagram does not show it listed for this model, how does it come off ? Also under it the shaft is similar to the nut/ spacer that I can't get off, almost square but all 4 points are different and it is kind of scalloped in between the points. Any help would be appreciated....................................... .................................................. .................................................. ...............................................OK, I just went to youtube and watched a video, it looks like the stock pulley has the odd shaped center section ( kind of square but not round like the replacement pulley I bought) so I just have to pull it off the transaxle..........what is the best way to pull that pulley off and can it be done while still on the tractor or do I need to pull the transaxle? I have a torch and will try heating it up and using a gear puller to get it off the shaft tomorrow unless someone has a better way to do it.