I am writing from Austin, Texas where your story* reached me via twitter.
I know Fishbourne from the time I lived in the UK and having performed there as a visiting Ermine Street Guard member. I am also familiar with the broken portrait bust. The suggested identification of the bust as Nero is intriguing, but I must question its comparison with the bust referred to in the article and the inset picture captioned as "The head of Nero in Musee de Louvre, Paris". It most likely isn't.
The bust in the Louvre is identified as Nero Claudius Drusus (often better known as Drusus the Elder). The bust is made of Parian marble, dated to ca. 9 BC–2 AD and came from Athens:
Iam writing a biography of the life and exploits of Drusus the Elder and his wars of conquest in Germania (12BCE-9BCE) for publication by Pen and Sword Books Ltd. I have been confused myself more than once by the recurrence of the same name. There were several men bearing the name Nero Claudius Drusus within three generations: to avoid confusion, theyare labelled by historians Drusus I (or the Elder), son of Tiberius Claudius Nero and Livia Drusilla; Drusus II or Julius Caesar Drusus, son of Drusus the Elder's brother Tiberius (and the future emperor) and Vispania Agrippina; Drusus III (known as Germanicus on account of his father's victories in Germania), son of Drusus the Elder and Antonia Minor (Marcus Antonius' daughter). The full name of the boy Nero who became emperor was Nero Claudius Caesar Drusus Germanicus. It is very easy to be confused!
I fear that Dr Rob Symmons, curator of archaeology at Fishbourne, may be confused by the name. It would be a pity for the distinguished team of Dr Symmons and Bournemouth University lecturers Dr Miles Russell and Harry Manley to run scans on the Fishbourne head and recreate the damaged parts of the face, testing the theory that it could in fact be the emperor, when the bust they are comparing it against is a completely different Roman.
Finally, just to correct a typo: the Iron Age British client "King Togidubnes" is correctly spelled Togidubnus or Togidumnus (he used to be called Cogidubnus).