Your t-box should be ok with all the parts there. Your best bet for finding a shifter is from a junkyard. Just be sure to tell the junkyard that you need the shifter, the cable AND the little arm that attaches the cable to your t-box. The one that the dealer shows in the parts catalog is incorrect. If you get a shifter from a 2004 you can also just remove the little solenoid that will come in the hanlde. You won't need it and it gets in the way trying to install it.
The only way to get that little arm is either buy the entire cable from the dealer and it will come with it or make one yourself.
Cutting the wires on the SLABS ECU isn't a big deal either.
As for the website, search google and you should find it. Don't have the link handy but its from a private Disco owner in the UK. Very good color photos and detailed instructions.