Searching for Henry Wallace

My gr.grandfather, Henry William Wallace was born in Galway, sometime between 1832 and 1842, depending on which of his Australian records can be relied upon.  I have not found a shipping record, but there are lots of unconfirmed possibilities,  H. Wallace etc.  He consistently gives his parents as John Wallace, gardener and Mary Cummins and gives Galway as his place of origin.  Henry was in Australia by 1868, when he married Catherine O'Brien on 8 September, at St Mary's Cathedral (Catherine was daughter of Kilkenny blacksmith Edward O'Brien and his wife Mary nee Hearney (sic). A witness to the marriage was William O'Brien.  Henry was literate and he was Catholic.  On 7 August 1871, he joined the NSW Permanent Military Force infantry.  This was a new force being established to replace regiments returning to England and Henry enlisted immediately, with his Regiment Number being 2, and he served as garrison orderley from the time of the enlistment.  This indicates prior military service, as according to recruiting advertisements of the time, preference for enlistment was given to men with previous military service, who were required to provide their prior service record and discharge papers.  I also remember, as a child, a photo of Henry in military uniform, red coat gold/buff facings. However, Henry deserted on 22  October, 1872. I  searched the Regimental records where I found a Henry Wallace from Oughterard, Galway, enlisted in the 40th Regiment of Foot, on 24 November, 1854 (number 3494) at the Galway Headquarters.  He was Catholic, 5'8" with gray eyes and dark brown hair ( a very similar description to that of my Henry).  He served in Victoria, NSW but deserted 26 December, 1857; recaptured, and returned to the Regiment in NZ during the Maori Wars.  This Henry Wallace is recorded as discharged on the NZ Medal list of 1869 and the Regiment commenced its return to England in 1866.  I was just about convinced that I had found my Henry, however a recent paid search in the UK National archives Regimental muster books indicates that Henry Wallace of the 40th Regiment returned to England, where he was discharged in 1867.  This does give time for him to return to Australia and marry Catherine late September 1868, but makes it less likely.   Catherine died young, in 1879, and my Henry married Winifred Daltan, of Rathdrum Co. Wicklow,  (my grandmother) 2 August 1880 in Sydney; they had four children.  I have travelled to Galway several times and have searched all of the records that have been available, but to no avail.  I have locvated a number of John Wallace' in the Griffith's Valuations in Galway, largely Kilcummin, but have not been able to locate a marriage of John Wallace and Mary Cummins, nor any siblings.  I would dearly love to locate a definitive place of birth and would be very appreciative of any advice or information.  Gloria Wallace