I don't think the KDX trans fits, I think in about 94 there was shaft size change. I have put the 98 1'st gear in my 99 and a friends 01, it gives you a lower 1'st gear and works well. The motor I have in my bike right now has 98 1'st and 2'nd and 02 3'rd 4'th and 5'th, the best combo I could come up with, there is a small gap between 2'nd and 3'rd but not bad. The 02 has a lower clutch gearing so in the end it is almost like a stock 98. I have both clutch baskets and drive gears, right now I am using the lower 02 clutch gearing with 13/48, with my 98 1'st and this setup I have almost the same 1'st gear as you do now but I have a stock 02 5'th gear. I watch egay and got my parts there. I also run a 13oz flywheel, rad valve and an EG 310. I only trailride. Just the 98 1'st gear makes your 01 a much nicer trail bike. Good luck Ed