thats a real clean 400ex. I just sold my 2001 about 2 months ago (miss it a lot). It is the most reliable quad i have ever had. I don't think there has ever been a better wheelie machine than the 400ex. It looks like ZSK from michigandirtsligners old 400ex.
As far as the exhaust goes, the muffler is stock but the header looks after market. Sort of looks like a pro curcuit header but it's hard to say. Anyways have fun and always wear your helmet and boots.