"the attack was quickly described by authorities as having "the hallmarks of Al Qaeda," in the sense that it involved synchronized strikes or sophistication in planning"
Almost any successful bombing is likely to involve sophistication in planning (think of the OK City bombing). So, that isn't much of a hallmark, really. And I think the IRA did some synchorized stuff, back in the day, for just one counter-example there.
On edit: Regarding the IRA use of same day bombings.
1982 July 20th. Great Britain, London, Hyde Park: The Irish Republican Army (IRA) exploded two bombs, one at Rotten Row, Hyde Park and the other at the Bandstand in Hyde Park, killing eight British Soldiers; three other soldiers are reported to have died later of their injuries.
The first bomb exploded when soldiers of the Blues and Royals were traveling on horseback to change guard at Horseguards Parade. Two soldiers were killed and 17 spectators injured. Seven horses were also killed by the explosion.
The second bomb had been planted under the bandstand in Hyde Park and the blast killed 6 soldiers of the Royal Green Jackets and injured 24 people.
http://www.disaster-management.net/bomb_ireland.htm