Just checked my P-5 plate for you. You just have to set some groves in the plate from the back. 2.5X2.5 mm, outside distance is 35mm, 17,5mm from the center scew. Then you can slide the upper rail's rims into the clamp and fix it with the upper rail knob.
You could leave this plate on your camera and use it without problems on the upper rail as well as on your ballhead/tripod.
To be sure just measure your rims in width and height on your NN3. Inside is not rectangular. Just added some groves to my plate and it works. The thread of the upper rail knob is a bit too long, add some metal washers below the knob or shorten the thread. I'll send pics tomorrow.
Be aware the clamp of ballhead/tripod really is an Arca Style Clamp.
Last edited by hindenhaag; 11-19-2012 at 09:47 AM.