Yeah.. Ang. There are two answers, a strict formal legal one, and a will I get away with it one?
'Dark Island' is such a simple and adaptable tune that its spread round the world and fallen into different cultures. Its sheer popularity has undermined a lot of the tune's copyright. You have this problem that even the publishers and copyright societies can't really fully control it, especially with 'youtube' and streaming. Nearly 60 years of popularity mean most people have heard it, and its entered into consciousness - and some cultures have been hearing it anew due to the Internet and 'Youtube'.

Anyway, it would be great if you added something to the world by creating a new original song!