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There is a Christopher Wall baptism (the only one) on irishgenealogy.ie (a free website for Dublin records) that lists a baptism year of 1761 to parents James Wall and Margaret (last name not recorded). Sponsors are listed as Luke Wall and Brigit Fitzsimons. Christopher was baptised in St. Michael and John's Parish, Dublin. There is not way of knowing if this is the correct Wall ancestor though. There doesn't seem to be any other children baptised of these particular parents so I have no way of knowing for sure if the above is correct. In the same way, the other James Wall baptisms listed there may also be relevant:
You may have to undergo an information gathering exercise as you did with Christopher to see if you can find out more about James through newspapers etc. If one brother was a doctor we could assume that the other also did well and and so there may be additional information available.