Here is the guy to contact if you want a very simple way to mount 17" wheels on your old-gen Ninja250...
His name is Jeff, he races with WERA,
jjuskowich@hotmail.com
I believe he charges $150 for the whole kit (front and rear). So a person could quite simply buy a kit from Jeff, buy a set of wheels and tires, then bolt them on, torque and saftey wire as needed.
The stickiest tires available for the old-gen bikes too, as simple as that!