The South Wonston Long Barrow is a cemetery consisting of three long barrows dating back to 5,000 BC and two Bronze Age round barrows from 2,000 - 1,000 BC. The people who built the barrows were among the earliest farmers in Southern Britain. These early farmers chose to bury their dead on a crest of chalk downland midway between the River Dever to the north and the River Itchen to the south.
The co-ordinates are from the information board at the Long Barrow: The main photo was taken in AB46; the reference number for Larkwhistle Farm = C; the date when Larkwhistle Farm was investigated = 19D9; the original height of the Long Barrow = Fm; the number of words in the board title = G.
The final cache co-ordintes = N51o (C-G)D. CFG, W001oAB. (C-G) AF
You are looking for a small clip-lock plastic container big enough for a log book and small swappables.