The co-ordinates supplied are for the Carnser car park at Blakeney Quay. There is a charge to park here unless you are a National Trust member.
The answers to all the clues are to be found in the proximity of the Quay.
The Cache is hidden at : North 52 degrees AB.CAD East 001 degrees 0F.GBG
The missing figures can be found as follows :
The Highest Flood was in 19AC
The other 20th century flood was in 19BD
The Guildhall Undercroft dates from the FG00's. You can get this information from the board outside the door.
To check you have the correct numbers: D = A + C and C = G - F
You then have a roughly ten minute walk to the cache.
Please note the National Trust does now allow dogs onto this site, but they must be on a lead..