After a glance at the pictures it appears to be an interesting bitsa truck (I often think of the bitsa trucks as being more interesting than a stock truck).
The truck has a civilian frame and seeing screws for mounting the lights it has civilian turn signals, tail & parking lights. And I don't think I've noticed amy military trucks with the deluxe bonnet. So my guess is a civilian truck made up to appear military, supporting newer front wings, Defender front doors with roll up windows, Defender door hinges & side mirrors. And of course a Defender style grille.
I agree, the first thing you are likely to want to do is add side windows to the hard top. The truck is slower than modern traffic and you need to be able to see what is zipping past you.
Manuals: Get the owners manual. It not only tells you what all the levers do but it provides the factory maintenance schedule and walks you stop by step through them, which includes all the tune up stuff.
Next you are going to want the factory workshop manuals. They will step you though the stuff not covered in the owners manual. The Hayes manual leaves a lot out and comparatively sucks.
The CD that British Heritage came out with a few years ago has everything you could need. But the copy protection makes it very restrictive. It will not work on a Mac nor will it work properly on newer Windows operating system. Personally I would rather have a paper manual out under the truck with me as it is more forgiving of grease, dirt and falling than a portable computer.
You can convert back to the original 2 headlight configuration but the earlier style front wing panels have been out of production for a long time and you would need to source an old original. It would be easier to source a newer style radiator bulkhead.
You do not want to use four headlights unless you install relays in both the high and low beam circuits or ran a separate set of wires for the second pair of headlamps. You would overpower the existing wiring.
An interesting truck and likely one with additional Defender parts as well. With a little luck maybe a previous owner put a Salisbury under the rear. It could easily be a nice fun to own truck but you need to go shopping for aftermarket add on wide windows quickly. Try your local RV accessories store or maybe look for camper shells being scrapped.
