You've posted in ANTRIM COMPLETED LOOK UP REQUESTS so this thread could easily get overlooked but just click on "report to moderator" to get this moved to the main ANTRIM board.
Not sure that you are aware of how difficult your request is. Civil registration of births, deaths & Catholic marriages didn't start until 1864 (from 1845 for non-Catholic marriages) so it means looking for church records. Not all of them survive and of those that do not all are online. There is no central index to find baptisms or marriages. Usually only the Church of Ireland kept burial registers (again not online) and it's difficult to find gravestones unless you already have an idea where to check.
Probably your best clue at the moment is the
“Intended place Of residence: Durham Street Belfast” dated 13 April 1869.
Looking at Google Streetview Durham St. looks to have been redeveloped (possibly after Belfast Blitz in WWII).
There are Belfast directories online but it's difficult to know exactly where George Smith intended to go without a street number. There is a Smith in the 1868 directory but that could be a co-incidence.
https://www.lennonwylie.co.uk/dcomplete1868.htm