12779/41 is the drawing number for "Watch Office, All Commands", which had two further revisions, 15371/41 (small front windows) and later 343/43 (medium size front windows).
Duxford has a "pure" 12779/41 tower.
Bury St. Edmunds tower is a 12779/41 modified to 15371/41 spec.
East Kirkby tower is a 12779/41 modified to 343/43 spec.
Martlesham Heath tower was built to 343/43 spec from new.
Let us know how you get on with the drawings from Hendon, I've had mixed results when I've had these sort of files from there.