The published co-ords are for Westow Park, this is made up of several private estates. Cache is not there.
There is a blue plaque nearby in the name of a person who spent a while in exile in Upper Norwood, they had been nominated twice for the Nobel Prize for literature.
Born in ABCD, they died in suspicious circumstances in EFGH
Cache can be found at N51 24.B(B-A)F W000 05.GG(F-H)
(Checksum for all numbers – 48)