Hey mate
Nice ute BTW
Unless there are different variants in the light housings and retaining rings?..
Not sure on that one myself.
However, to fix your problem if you are missing the parts?
Or if like mine were, rusted,broken of in the hole, some missing etc....
The picture you have posted is the same as my lights.
What I did.
For the retaining ring, ( holds headlight lens into the housing)
They are a fine pitch threaded screw. Something like an M4 size and thread pitch
You file them flat, centre pop the middle of screw and drill them of with a really small.
Say 2mm drill bit, avoid if you can damaging the threads in the housing.
Then collapse the left over part of the screw.
Using a thread tap of M4 size, clean up and re tap the thread into housing.
Or, drill the out with a 3mm or 1/8 inch drill bit and put some, I think 8g gauge self tappers in
Stainless if you wanted
The adjusting screws I was missing a couple, so I made some up for that also.
The nut, in the picture you posted.
Is actually a small plastic insert that clips into a square hole in the body.
Again around a M5 fine threaded size I think that one is longer screw
On the Phillips head end of this screw, just slightly down the shank.
There is a raised lip, (like a washer) the same size as the screw head.
So then the small fork section in the headlight housing slips between this gap on the shank of the screw.
Then when the screw is turned in or out.
It pushes the headlight housing in on out to adjust the beam.
Each headlight has two of these screws.
One for vertical adjustment, one for horizontal adjustment
If none of that makes any sense and is just too damn confusing.
I'm really sorry.
Maybe I could take a few pictures and post..
Let me know

Cheers