Here are 2 threads that might be of interest to you?

http://www.nsr250.net/forums/viewtopic.php?t=11032

http://www.nsr250.net/forums/viewtopic.php?t=8292

But for what it is worth, the length of an assembled MC18 R5k fork (with no load on it) from the centre of the front axle to the top of the stanchion is about 722mm.
What is this measurement for your forks? Are they '95 ZXR750 or 1991-4 ZX7R?

Also, if you do end up raising the drive sprocket (in relation to the rear axle), it may induce a bit more antisquat.
<edit> Actually, after thinking about that a bit, I think that is wrong. The NSR generally is set up to squat the rear suspension under power. </edit>
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...