Gilmour or Queen, County Antrim

I am looking for info on a James Gilmour. According to his marriage
cert he was 45 in 1917, so born around 1871-72 I think in Ballymena,
County Antrim. I have checked ancestry.co.uk to no avail. I believe he
left his home to fight in the Boer War (the second I presume,
1899-1902). He was some sort of engineer I believe. He then turned up
in Glasgow and married my ggrandmother in 1917. I know nothing of his
parents, siblings, or his whereabouts between 1902 and 1917. I am not
even totally sure his name was Gilmour as his daughter overheard an
argument once during which her mother said his real name was Queen, he
had changed to his mother's maiden name (Gilmour/Gilmore) and he had to

escape Ireland for some reason (rumoured to be IRA problems though
Wikipedia states no IRA pre 1919!).

Don Phillipson...

Wikipedia is reliable in this respect in only the
narrowest technical sense (of when the name
IRA was first used.) Irish nationalists were
active throughout the 19th century through such
groups as the Fenian Brotherhood (of which the
US branch launched an invasion of Canada in
about 1866.)

I would value any guidance on where else I might search for birth
details, whether Gilmour and Queen are protestant or catholic names,
whether he might have been in trouble if the child of a mixed marriage,

what army unit he might have joined (i.e. one local to the North of
ireland?) and any other information that might be relevant.

Hope you can help.