A park and grab for you in Mt Roskill. I've always found these roads fascinating...designated to be roads by the local Road Board back in the day, but never got around to finishing it. It's now a local cycleway through Mt Roskill, plus plenty of walkers and dogs out for a stroll.
Duncumb Street was named after a local councillor for the Mount Roskill Borough Council, having been renamed from Cross St, in 1975. You can find out a little about your local street if you're interested by searching on this nifty little part of the Auckland City website:
http://www.aucklandcity.govt.nz/dbtw-wpd/streets/streets.html
From here you are not far from the site of the Wesley Trust Estate, which ran a Native Institution in the area until the 1920s. You can see some of the magnificent original trees planted at the estate at Arthur Rickards Reserve off Parau Street.
You're looking for a very small cache, please be gentle retrieving me and make a good effort to put its lid on.