I'll take some under the seat pics for you to show you what all needs to be shaved down I used the stock airbox though...I also shaved the sides as well you don't have to but stock warrior fenders have an extra piece at the bottom riveted on I shaved these while they were on my warrior then just modded them to fit over the stock airbox the seat is a tight fit and you have to play with them a little bit to get them perfect alot of marking, cut, put on, then repeat.....
In this first photo you see two spots near the center where I put bolts through and small nuts with washers on the other side your seat will hold the rest but there is two other spots im gonna get to. I know I need bushings for the ex shock I just sat it on to see airbox clearance.
Now you need to cut some up front.
now drill a hole on each side at the bottom mount
If I shoulda posted this in the diy let me know and I'll move it!
my friend has a complete set of 400ex plastics on his blasty but i wouldnt reccomend it because you have to drill out a new hole for the gas cap. the front plastics look fine but the back ones are too big and floppy for such a small quad
your best bet is to keep the plastics stock. mod/cut the stock fenders to the design/style you would like.its a hack, but a little time and effort in designing, it can look good.