The pair have been made available for permanent transfer or immediate loan from the League Two side, who have undergone numerous personnel changes during the summer.
Williams joined the Magpies on a free-transfer signing from Manchester United in March last year, however, the 22-year old has failed to make any of Thordarson's first-team squads, while 29-year-old Scully has also failed to feature so far this season after joining from Barnet in February 2004.
Both are contracted until June 2005, but leave the club earlier as Thordarson looks to shift out the deadwood.