Mr Big (31) and the 47-year-old gangster who is blamed for introducing Tiger kidnapping to Ireland are the chief suspects for planning the murder of Alan Ryan last September.
Police raided the Enniskillen property where they seized forged documents, including driving licences and passports. They also confiscated over €60,000 in cash which is believed to have been buried.
Both men are expected to face multiple serious crime charges. The arrests happened as part of an intelligence-sharing operation between the Garda Organised Crime Unit and the PSNI's Organised Crime branch.
It is understood the older gangster had grown a beard and had taken to wearing disguises. The two thugs are the number one targets for the Organised Crime Unit and are strongly suspected of ordering Ryan's murder after their gang got into a feud with the terror chief after a nightclub assault in December 2011.
This led to several tit-for-tat incidents which included a foiled murder attempt, a number of savage assaults, death threats swinging back and forward and Ryan's mob stealing a huge cash sum from the drugs and Tiger kidnap gang.
Sources say that by last autumn the crime gang decided "enough was enough" and hatched the plan to have Ryan shot dead in broad daylight in Clonshaugh, north Dublin.
The Herald understands that 'Mr Big' was in Spain when the murder happened in early September while his veteran criminal sidekick was in Co Cavan.
'Mr Big' had been based in Spain since April 2012 because of his feud with Ryan but he returned to Dublin in December as his gang regrouped and decided to take on Ryan's RIRA mob head on.
Within days of his return, 'Mr Big' was arrested in a car in Dublin with his right- hand man. They were later released.
In the meantime, the veteran Tiger kidnap gangster was forced to relocate to the North because gardai sought him after a number of bench warrants were issued for his arrest.
In the last two months, the two gang bosses have continued to direct operations and have stepped up a campaign of terror against what has been left of Ryan's RIRA mob .