Here is a picture of a tool made for removing the drive nut. With the tractor in high gear and the brakes set you can unscrew the drive nut from the tramission counter shaft. With the square key of the tool in the slot of the nut, as you put a little pull on the tool take a hammer and tap on the nut.
I also have a tool made for removing the nut from the pump, but I can't find the picture. I took an old inpact socket that I welded a piece of key stock to that fits the nut and with the air impact wrench I have been able to remove the nut from the pump without any disassembly of the pump assembly.
Hope this helps, charlie