Don't go taking it apart so quick.
Your Ninja disc won't fit the "3 groups of 2" bolt pattern on your TW wheel. No how, no way, short of having an adapter plate machined. Then you'd need to have a plate machined to move your existing caliper to the rear so it will clear the new disc, and have it returned to the correct offset.
Lotsa work and cubic dollars.
There may be an existing kit for one of the few other bikes which share our bolt psattern. Early YZ80's Xt's and TTR's are among the few but there probably isn't much demand.
Cubic dollars again, but complete kits with less chance of you ending up room temperature.