What a brilliant puzzle. Definitely one of my favourites.
It turned out that I had actually got the correct identities of A-D a couple of months ago. The problem is working out the link between them. The clue from CMs night cache was the breakthrough, and the numbers are then obvious.
We searched for about twenty minutes without a GPS but gave up. The hide is very difficult. Using a GPS it indicated a likely location and the cache was in the first place I looked
Took nothing but the finders certificate, left a fossil sea urchin from Morocco.