At the coordinates you need to find the plaque on the foundation stone and the cache can be found by answering the following questions:
S39 11.ABC
E175 32.DEF
A = The number of letters after James Gunson’s name
B = The Chairman’s middle name
C = Add the 2 digits in the date together (before the month)
D = Month
E = Surname of the Architect
F = Number of letters after J. Cullen