Many thanks for the post – and welcome to Hong Kong Outdoors.
I put some info on the redoubt in article on Kam Shan Country Park – but when I visited, didn’t enter tunnels (beyond main command post), as too darn spooky!
Found booklet by AFCD, on war relics in country parks, very useful: has map inc tunnels etc of the redoubt.
For people interested in war relics, a recently opened trail at Wong Nai Chung Gap is worthwhile – has info boards, and passes old anti-aircraft battery position, pillboxes etc. I’ve walked it, and been meaning to do article for this site … sometime. (Walked it for new guide booklet coming out from HKTB.)