Sykes, who was appointed at the end of October, was with Callinan as a player at Forest Green Rovers.
And Callinan was previously manager at The Causeway from October 2002 to October 2003.
Also well-known in the area as a former Gloucester City boss, Callinan will also take the Cinderford bag as physio as well as helping out with coaching.
As a player, he started out at Cheltenham Town and then turned out for Cheltenham Saracens, Cinderford, Gloucester and Forest Green, where he was a member of the side that won the Southern League Southern Division title in 1996/97.
More recently, he has been with Uhlsport Hellenic League Premier Division side Longlevens as physio and coach.
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