Robert, you need to buy James Gibson's marriage and death certificates, which you can do online at http://www.bdm.nsw.gov.au/familyHistory/search.htm

NSW certs are very informative with ages, occupations, addresses, and usually include full details of both parents and their addresses.

Is this his marriage?
2398/1863 [regt no/year], GIBSON JAMES [groom], GILMORE SARAH F [bride], MUDGEE [district].

You need to buy both marriage and death certs because each will add to the information you need to trace back to his place of origin. They should also show how long he had lived in Australia at the time, so that you can find his passenger record.

Sue