Frank, upon thinking about the evidentiary uses that you will be using your D3 for once you get it GPS equipped, do make sure that your GPS unit is one of those that can pass on the bearing of the camera as well as the coordinates, height and time.
The bearing information helps establish the direction that the camera is being pointed in when the image was recorded.
For example my Holux M-241 GPS doesn't pass on the bearing information, even though my cameras and the foolography and AOKA bluetooth units that I have can deal with the heading information. The GPS units that you need for the bearing information are those that clip onto the flash bracket.