The gun emplacement was on the highest ground on top of the cliffs on the southern edge of the quarry, but the concrete floor shown above (a hundred or so metres south of the gun site) could be WW2 and something to do with the Wellhaugh guns?
It could be possibly be just the concrete floor Public toilets as they are shown on later maps but I think the position is wrong.
On the subject of the Guns at Wellhaugh AKA 'The Amble Battery' I did ask the National Army Museum if they had a picture but the don't have one unfortunately.
English Heritage notes on the site