I also noted I the manual said I needed the special clutch tool. As I remmber I just used a hammer and a cold chisel to knock it loose because I didn't have one. I did use a torch to heat it up to loosen too.
The problem with getting the center nut lose from what we used to call the clutch boss is that the boss itself will turn, the clutch tool is a tool that is made to hold the boss so you can get its bolt lose.
You might be able to us an oil filter wrench, or a strap wrench. I never bought a clutch tool, but I have made them.
The last one I made I used one of the old metal clutch plates and welded a piece of metal to the face and edge of it for a handle. The metal clutch plate is splined to fit the teeth of the inner boss.