Not sure if my setup will give you any inspiration or not.
I have a np231/d300. the d300 shifters went right through the factory hole.
The np231 is shifted by a small air ram.
post 55 and 56 has some info
http://www.rme4x4.com/showthread.php?83436-Nathan-and-Tanja-s-99-XJ-Build-up/page4
let me know if you want more info, it wasn't exactly cheap, I think I have about $125 or so in the whole setup. (and it obviously requires and air source)
The ram shifts the np231 from 2h to 4l, without any stops in the middle, so I can't put the range box in neutral, it has not been an issue since I can put the other two boxes in neutral.
post #62 has the d300 shifters
post #72 has the switch for the air solenoid.
I don't think I have a picture of the air solenoid.
Nathan