Griffith Valuation of 1862 is now a census substitute, originally a valuation for taxes. A Thomas Brown is not listed as as its too early, most irish stayed at home till marriage when they would leased their own land.
Drumkeeran was a Parish and a townland in the Poor Law Union of Irvinestown (any parishes and villages, townlands within 12 mi. radius of named town)
There are Browns listed in the Union of Irvinestone in the Parishes of Magheracross,
Magheraculmoney and Derryvullen. Names Anne, Tobert, Henry, Mary, James, Edward, John and Samuel.
Drumkeeran might be the Gibson's home Parish as usually marriages took place in the bride's parish.
There are Gibsons listed in the Parish of Drumkeeran, names Andrew, Samuel, Ephraim, William and George. (look to the names of Thomas and Anne's children as they would of named
their brood after familes, 2nd. son would probably be named after Anne's father (*Andrew)
You can be proactive while waiting for a family contact. Don't forget to keep your contact email address updated while waiting for this contact.
Both names are in the Fermanagh County for the british telephone book - Northern Ireland.
None specifically with any of the place names listed. You could pick one from each area and write letters, the phone book gives a full mailing address with a postal code. A good map maybe of help, look for the town names listed and how close to Irvinestown they are.
There are two sources of parish and civil records to about 1900 depending on parish.www.rootsireland.ie
and (birth record will give mother's name and maiden name)www.emeraldancestors.com
Also civil bmd's www.familysearch.org
if you are lucky they may have the couple's father's names listed.
Thomas Brown marriage Jan 8, 1864 #293 Civil Registration number (see PRONI)
Fa: John Brown Fa: * Andrew Gibson
With this number you should be able to get a copy of the marriage certificate if you want one.www.igp-web.com
+ Fermanagh usually a good website for county information
Doubt this would be of any help as I think the parents would be deceased by 1901:
1901/1911 Census: www.census.nationalarchives.ie