My apologies for some of the earlier info - I didn't have the data in front of me. I do now...
According to his naturalisation papers (which my mother attained), Giuseppe Guglielmini was born in Spalato, Italy on 20th August 1928. He died under the anglicised name of Joseph John Williams, on March 2 1977. According to the death certificate, his father's name is Rudolfo Guglielmini and mother's name (maiden) was Catherine Beric. The trouble here is that the death certificate lists the birth location as Spolito, Jugoslavia.
My error previously was that Giuseppe was my great-grandfather - he was in fact my mother's father.
Lucilla Stefanovich was born at Villa Decani, Italy on 12 October 1928. Her parents were Rosalia & Gianpolo Stefanovich (I do not know Rosalia's maiden name).
Of all the info I have, this is pretty much it. I'd like to try and trace the Stefanovich & Guglielmini lines as far back as I can, and also try to track down any living descendents. I do not know if Giuseppe had any siblings, but do know that Lucilla had two sisters - only known to my mother as Aunt Nellie and Aunt Anna.
Oh - one more small detail. The naturalisation certificates were signed in 1959, with the "Alien Registration certificate" dates in early June 1954.