Hugh, I am not sure which website you can't access, but they all work for me. If you could access the Garden of Remembrance website, you could ask them about your ancestor yourself by clicking the "Contact Us" button.
Anyway, your ancestor does not appear to be indexed on austcemindex, for whatever reason, nor on the Ryerson Index which indexes death notices in Australian newspapers. I will ring the G of R and ask about his ashes. If there is indeed a plaque and the ashes haven't just been scattered, I will get out there sometime and try to take a photo. It won't be straight away, because we are having an awful heatwave, not the kind of weather to be plodding round cemeteries. But I will get there when the weather improves.
Marie