This pillbox is shown as 'PB3' on a hand drawn map included in the War Diary of Major E.G. Stewart. I'm not sure if 'PB3' was the 'official' reference for the pillbox or just his personal numbering system, as there was another Pillbox number 3 on the Western shore of HK island, between Sandy Bay and Telegraph Bay.
I was in Stanley this afternoon, and remembered there should be a pillbox around here. Sure enough you can see the square loopholes just above the shoreline. Here's the view across from Murray House.
A trench system with over 10 pillboxes built by the Japanese
Exact location is not sure. But it must be in the square formed by the Green House to the west, Kennedy Road to the south, the fountain to the north and the park entrance to the east.
It is possible to be built by Japanese. The quality of building material is very bad and it is not in British style.
PB 17, Repulse Bay
The above map for this place isn't accurate, as I'm not sure exactly where it is. [Update Jun 2008: The location is accurate now, confirmed by this map from the HKHAA.] This week's HK magazine has an article 'Tearing up the town' about historical areas that may be redeveloped and disappear. Their description of Tai Hom Village, Diamond Hill says:
See photos & notes here.