Take a look at the picture below. The top one is a stock TW200 output shaft. The middle one is a modified TW200 output shaft. The bottom one is a stock XT/TTR225 output shaft.
The modifications to the stock TW200 shaft involve grinding an additional circlip groove and the fabrication of the spacer/washer shown on the center image below.
If this is a job that you would like to try and tackle, I could send you the above XT/TTR225 shaft and the modified TW200 shaft that you could take the actual measurements from.
Let me know if you are interested in doing this,