I mentioned when discussing the High Light that the pair had survived because of a feature of the Low Light.  Unfortunately, the feature in question isn't visible in this photograph but I will make a point of getting a shot of it on my next visit to this site.  The range pair were future proofed by the simple expedient of mounting the front light on rails - as the channel they were designed to mark shifted, the front light could simply be jacked sideways along the rails to realign the range.