Thanks, that's a useful picture for many reasons! Unfortunately it doesn't have the internal panelling in place, so the rear light protection is not evident. I think I've found one on the CSXinfo site that helps, if this is not a modified car:
csxinfo.net - Photo Gallery
The side wall of the trunk angles away from the framework tubing, with a pop-riveted panel, so the back of the light is inside the trunk. As Kirkham make it, the aluminium panel continues straight, against the tubing, leaving the light out in the wheelarch. You can imagine what would happen to that bulb when the stone chips start flying!
Time for a bit of surgery...