i've been trying to do this for a few months now, if you can be bothered looking back a few pages there should be a thread.
i had a good look around the wrecking yards, and i havent been able to find a suitable donor tail gate.
i was actually looking at hinges and locking mechanisms, but still, most hinges are welded into the tail gate, and so if you want, you'd have to cut them out of the door.
i will be making a custom door for my vitara, as both sides are not the same, as in the left side, where the lock is, and the right side, where the hinges are.
also, you can, but dont think its a good idea to use the existing vit hinges, as they are not exactly the same.
i will be getting some big-ish trailer door hinges to put on, as i'm looking at making the rear door removable as well.
in the rear door, there is the handle, and lock mechanism, not sure if you still want to use something like this, chances are it'll be way too complex to be worth it. and the lights, meh, this is easy, re-route the wiring to where ever you need.
i will be looking into some trailer latches too, on the outside maybe, and on both sides. like Mr. Bean on his mini maybe.... anyway.
i'm just waiting on some time and money to come around before i start. have a look at the tail gates on the new holden crewmans, they are similar to what i may be using.
and to hold the tailgate up, i'm just gonna use some chain on either side of the door, but maybe both.
as for the spare, i havent carried a spare in my vit for over a year now. touch wood. but if you still want a spare, you'd probably need to get a custom rear bar/bumper made up, so you can attach a swing away tyre rack thing. sorta defeats the purpose of having a drop down tailgate. i just chuck my spare inside, i have no back seat.
later.
also, saw ur post out outerlimits, this should answer it too. outerlimits isnt that great when it comes to vitaras in general, but anythin zook is always good.
cheers
Steve