In 05 the KX250 got a complete overhaul from the earlier 03/04s. Except for the plastics,(Tanks are different also), clutch plates and a few other things the 05-07s are completely different. Frame is narrower by about an inch in the foot peg area. Engine is new from the cases up. I have a 03, 04, 07 and my 04 500 hybrid. The 06 and 07s have a quirky handling trait, there is a thread going in the 250 forum. I think it would be worsened if the 500 were put into it. I havent measured the width of the engines but I wonder since the frames are narrower on the 05 up bikes will there be any brake pedal interferance? I thought about doing a conversion with the newer chassis but see no real advantage. If you want the later suspension components the forks and shock from the 07 will bolt on to the 04. The shock length is different between the 03 and the 04-07 due to the different linkage arrangement in 03 so I wouldnt put the 04 up shock in it. Cant remember if it was shorter or longer. Forks will fit though.
