I would just stick with the 5 speed if your trying to keep the money down, the 5 speed is a tougher trans. I hope Lee is right about the 98 and up motor working, he said a 03 and up KX pipe fit 04 cr125,s and up, the 03 KX pipe is not even close to fitting on a 04 Cr 125. I went out and bought 2 2003 KX pipes, Doma and HGS BUd, hope you have better luck. The head stay from another year will prob be different too.