The location of the marker is a rough guess, baded on Lawrence Tsui's note that it was on Portland Street:
I only know that Post Z Kwong Hang Stall was on Portland Street near Yen Chow Street. I've not been able to identify the exact location or house number. None of the legends written on the Guerrilas and the shop mention the exact location.
One person who might remember is Wong Chok-choi who is living in HK. He is the younger brother of Raymond Wong Chok-mui (No.99) who was the chief liaison officer of the Red Guerrillas with the BAAG. Post Z was set up under a pseudo-name of Raymond Wong. As a teenager, Wong Chok-choi worked at the shop as a shop assistant. His father & elder sister also worked there. He was arrested when Post Z was raided, and detained for a few days at the Supreme Court before being released. He claimed to have met Selwyn-Clarke & some other BAAG agents while detained. After he was released and Post Z came to an end, he was called to work with the Red Guerrillas north of the border where Raymond Wong was active.
BTW, Raymond Wong MBE (No.99) perished with others in the bombing of Air India flight Kashmier over the sea near Indonesia early in 1955. It was an assassination attempt against Premier Zhou Enlai who was tipped off not to take the flight. I have been in contact with Raymond Wong's wife who is living in Beijing and his son in HK. However, they were not any more knowlegeable since the marriage happened after the War. Raymond Wong's eldest sister may know although she is very hard of hearing when I met her several years ago.
Wong Chok-choi worked at the NCNA-HK aftet the War. He has since retired and has been keen to write legends about the Red Guerrillas. He is still living and well in Hong Kong.