The OEM tool is 57001-242, I think. The thread pitch is 27mm x 1mm, left hand thread (reverse).
I have an inexpensive Dennis Stubblefield Sales tool, and it works great.
In case someone finds this thread in a future search, the same tool works on 1989 and newer KDX200 / KDX220R / KDX250 models. 1988 and older models don't have threads in the center, so the tool won't work. The plate and three bolts type puller is used on those.
The rope trick or the Steahly Offroad engine lockup tool will come in handy when removing the flywheel nut / bolt.
I got the nut off using a rear set of passenger pegs from my street bike and the top engine mount bolts to hold the flywheel (don't ask). Now I just need to get one of these and a large socket for the clutch nut. Thanks again!