The tiles, so I understand from members of the Friends of Waikumete Cemetery (as mentioned on the 30 October walk), are a recent upgrade. It is certainly a grave almost impossible to miss, now.
Here's what the Te Aroha News published as a obituary (from Auckland papers), 9 March 1889:
Another well known resident and also an old identity, has just passed over to the great majority, in the person of Dr. Wm. Stockwell, who died at his residence, Symonds-street, yesterday evening. Dr. Stockwell had been ailing for some considerable time previously, and three or four months prior to death he gave up his public practice, which was an extensive one. His complaint was heart disease, and he was attended by Drs. Mackellar, Philson, and Roberton, while other members of the medical profession paid the invalid every attention. The doctor was afflicted with heart disease, and it proved incurable. A change for the worse took place in his condition on Saturday morning last, and from that time till the end he sank gradually, retaining his consciousness till the last. Dr. Stockwell came to Auckland over twenty years ago, and soon established a good medical practice. Prior to arrival hero he had been an army surgeon and served in the Crimea, In Auckland he was for some time a member of the honorary medical staff of the Auckland Hospital, and he also acted as honorary surgeon to several benevolent institutions. The doctor also took an interest in farming, and he had one of the best-situated farms in the Waitakerei district. He passed away at the early age of 57 years. Dr. Stockwell was highly popular and respected by all who know him, and his death will be generally regretted.