I think this might be the family in 1881 - thank goodness for the name Rueben among all these Marys and Williams! So there were two Mary's as Jenn has suggested.
1871 21 Britannia St St Pancras
William
Orford 30 Head coachman b Marylebone
Mary Orford 30 wife b Cripplegate
Emma Orford 9 - all chn b Pancras
William Orford 6
Frederick Orford 5
Jane Orford 3
Mary Orford 8 months
1881 51 St James Rd, West Islington
William
Orford 40 Head Cabdriver b Lambeth
Mary Orford 40 wife b City of London
William Orford 16 Blacksmith assistant b Bloomsbury
Jane Orford 13 b St Pancras
Mary Orford 10 b St Pancras
Ruben Orford 8 b Islington
Henry Orford 2 b Islington
And I would think this is William's death in Qld
1883 William Orford, parents: John Orford, Mary Wigley #15885
Thus the immigration would be between 1881 and 1883.
The daughter Mary's birth:
http://www.freebmd.org.uk/cgi/search.plMary Caroline ORFORD, reg Pancras 1b 69, Sep qr 1880
I think I can find Mary C Stone (the mother)in 1851 and her birth - do you want them as well??
Judith