Gerard Houllier's backroom team announced
Former Scotland international McAllister, capped 57 times, was described by the new Villa manager as "my most inspirational signing" during their time at Liverpool where McAllister played an integral role in the unique treble triumph of 2001 (Uefa Cup, FA Cup and League Cup).
He has also managed at Coventry City and Leeds United.
Villa legend Cowans, who was capped 10 times for England, joined Villa as an apprentice when he was 15 years old and in three spells at the club made a total of 527 appearances.
He won the league in 1981 and the European Cup in 1982 and has been coaching Villa's youth for many years.
Rafa Gonzalez, who came to the club in the 2007-08 season as goalkeeping coach to the reserve team, will be goalkeeping coach and Robert Duverne, who worked with Houllier at Lyon where they won back-to-back titles, will assist as coach/fitness coach.