the first time I removed the fan clutch I used an air chisel and just tapped it off but I discovered the nut is only a thin walled nut and is easily damaged with the air chisel so when I replaced it I used a wrench. once its loose it just spins off.
This is what I used $16 from Northern Tool. Place the longer wrench in the set on the nut with wrench handling pointing toward the sky and then a few taps with a good size hammer to the left as you are facing the front of the D2. If you need a little more leverage, put a breaking bar in the hole on end of the wrench to make it longer, and repeat.
After renting the "fan tool set" from the local auto-parts place I found that they never really fit correctly. Seemed like a sloppy fit and after a couple try's it just rounded the fan bolt and didn't always loosen the fan. That pic above looks like a nice set of wrenches!
I found this tool to help and always did the trick. It's an 1" and 7/16's box end wrench from the local tool place, in this case Tool King. It fits snug and with the belts still on, you slip it on the nut and give it a whack with a good size hammer on the rounded side, just to the right and away it goes, it has never failed yet. Just remember to leave the belts on so there is tension on the pulleys.