go with the kxt head on the kx cylinder, a nice kx ignition is key as mentioned, but if you got the cash, go with a pvl ignition. 38mm airstryker carb, some v-force 3 reeds, you got yourself a sweet set up. dg is an ok pipe, but try and find something better if you can. some progressive springs in the forks, and an extended swinger with a 300ex, or raptor shock, should get that thing riding smooth. and yeah, get some smaller rear tires. i got 18" fast trekkers for mine.
1985 KXT 250 Tecate - kx cylinder, kx ignition, bassani headpipe, answer silencer, v-force reeds, 38mm airstyker carb, +2 franks swinger, raptor rear shock.
1996 YSF240 Blaster - maxxed out!!!
Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting "HOLY SH-T, what a ride!"