John, I got the same answer from a contact in the UK, they did not know the difference either. John McCallum may know???
Anyway I have installed the CS116 springs and ride height is now 310mm, (I too have 15" wheels, but rolling diameter is very close to OEM because of the lower profile rubber) which gives approx 50mm clearance from tyre to guard so alignment is done and car sits really well.
The outcome of this only reinforces my dislike for Burtons and their lack of giving a &^$#.