Well, if the lamps are the same as the latest spec, this is how they hang together.............
Note that this chrome bezel is a FRONT indicator bezel.
Here to the right of the bulb is a captive stud. Another is hidden on the opposite side.
On the back is the neoprene gasket and the nuts. The brass coloured tube is where the bullet connector of the earth wire presses in.
The lens is held in place with setscrews and brass "top hat" female fixings which fit from behind.
This photo shows the slot in the bottom of the housing and you can just see the small orange lug on the reflector.
Note also that the setscrews are longer on the front indicators than the rears and are a different thread!!!!!
This meant that when I changed my rear covers to deeper fronts on the rear, I had to get behind the chrome bezel to change the top hats, and I did this without disturbing the plinth on the wing. So although I don't recall exactly, I think the rears have small bolts which locate in threaded posts inside the plinth - instead of the captive studs shown above.
I hope that sheds some light.......