here is what i found on line about it
TarheelRedRider: No it was pretty easy, the hardest part is finding away to mount the rear fenders. You will have to cut the frame mounts where your old seat hooks mount. I used the 400ex seat but now that I think about it you probley be able to use the 300ex seat and mount it to the 400ex fenders and keep the mounts. I cut mine. But if your not up to hacking on the frame maier makes some new redesigned 300ex plastic that looks like the 450r plastic. It looks freaking great. I know that will be the way I go when its time to replace mine. Back to 400ex, yes I made my brackets, and a few zip ties work really good. You can buy a set of used 400ex brackets and just drill a tap the holes where you need to mount the brackets. But the 400ex plastic fits pretty good, just have to take your time fitting it in to place. On a scale 1 to 10, 10 hardest I would say a 5.
this is from a nother form that my buddy is on