Here's a more established link between John Mason and the Murnane family. In 1842, Michael Murnane's daughter Bridget married a William Dowdy (or Doody) at St Mary's Catholic church in Sydney. The Dowdy's travelled to Adelaide on the Dorset with the Mason family in 1845. (They are listed as Mr and Mrs W Doodey in this newspaper clipping.)
On July 7 1845 the Dowdy's second child, Michael Patrick, was baptised in Adelaide by Bishop Francis Murphy. One of the sponsors was John Mason.