Sue, your e-mail address would not work for me.I see from the Australian records that the marriage of William Henry White and Margaret Clancy in 1856 was at St Patrick's RC Church in Paramatta, NSW.
The only Irish record for a Margaret Clancy born in the mid-1830s that I could find was this (VRI) one:
++++++++++++++++++++++++++++++++++++
CLANCEY, Margarittam Christening
Gender: Female
Christening Date: 5 Nov 1835 Recorded in: Killucan and ballinameen, Roscommon, Ireland
Collection: Roman Catholic
Father: Danielis CLANCEY
Mother: Catherinae GANNON
Source: FHL Film 989741 Dates: 1833 - 1850
+++++++++++++++++++++++++++++++++++++
Mother in this case is Catherine, so you can probably rule this one out.
The only marriage of a Clancy male to a Margaret I could find in the VRI is this one. It's a bit early. However, if you are sure about the mother's name being Margaret, it is possibly relevant:
++++++++++++++++++++++++++++++++++++++
CLANCY, Thomam Marriage
Wife: Margaritam FORD
Marriage Date: 19 Sep 1816 Recorded in: Boyle, Roscommon, Ireland
Collection: Roman Catholic
Source: FHL Film 989743 Dates: 1808 - 1864
++++++++++++++++++++++++++++++++++++++
brianfw@ozemail.com.au