The online catalog is wrong it says there is now piston port window that's not true! The pro-lite pistons do have the window so they are okay to use. Make sure you do not order the part for the '03's! the piston's will not work and the gaskets kits won't totally work either. There's a difference in the base gasket I haven't looked into totally yet what the exact difference is I think it's just thickness. But the part #'s are all different the only part thats the same is the wrist pin bearing. The GP pistons are the one's without the piston port windows. From the KX's cylinder design I would recommend using the one's with the piston port windows. I just thought I'd let ya guys know since I've compared both the '03 and '04 parts back to back and there is a difference is piston design.