If you are happy to spend £12 a pdf of the 1964 pilots notes can be downloaded from here:
Westland Wessex HU Mk.5 Helicopter Pilot's Notes Manual - AP 101C105-15 - 1964 - Aircraft Reports - Aircraft Manuals - Aircraft Helicopter Engines Propellers Blueprints Publications
I assume you have tried the FAAM who have at least two HU5s?
I presume you are not referring to position 44 in the diagram JE posted as all the positions are itemised in the text. Are you sure they were not just plated over unused positions from new or just empty card holders?
If you can PM me the image you have I am happy to post it for you.