I came across this 1915 advert while researching Firth Brothers of Melbourne, who built several hundred - maybe 1000 - motorcycles between 1914 and 1925 or so. Mostly JAP powered, but they built their own ohv v-twin c1915, and an engine called the Monarch in 1920-21, which was a very close copy of the 6 hp v-twin Swiss MAG.
Their real expertise was manufacturing. In 1915 they had automated machinery capable of turning out piles of widgets at speed: one example was valve cover bungs, which could be turned out at 170 per hour.
Why they had Douglas TT Racing Cams for sale is a puzzle. Perhaps they intended to manufacture them?
Equally I wonder where they got the cams. "Just landed" suggests they came from the UK. Did Douglas sell "TT racing cams" in 1915?
Leon