Stan, if you are making your own adapter, looks like this guy in the seattle area already has shafts made up that will go from toybox to the d300. Its not what he intended them for but i think it might work. Heat treated 4340 blah,blah. Not sure if their long enough but it will be nice to just get an off the self part for your project. I am not sure if the spline angle is the same though???
http://www.pirate4x4.com/forum/showthread.php?t=451754
http://www.pirate4x4.com/forum/showthread.php?t=451754