Guess what...I received all the documents today! Record time I think. Anyhow, basically confirms much of the information you had put forward to me. my g.grandfather Antonio was the son of Diego Alessi (of Palma) and Maria Valenza (of Pantelleria).
The marriage record of Diego and Maria takes has now taken me back another generation; Diego's parents were Calogero Alessi and Onofria Alobiso while Maria's parents were Francesco Valenza and Ana Maccotta.
Thanks again for your advice and help!