Arguably the largest of all the bichirs is Polypterus endlicheri congicus which can reach up to 97cm (about 36 inches). There are historical reports of larger bichirs in the Nile River drainages reaching up to 5 feet but those are unsubstantiated.
The stripes and flat head would definitely indicate either Polypterus endlicheri endlicheri or Polypterus endlicheri congicus....unless the stripes are horizontal in which case it is probably one of the Polypterus bichir subspecies like P. bichir bichir (unlikely as these are really hard to get) or P. bichir lapradei. The Polypterus bichir subspecies are substantial bichirs as well....reaching up to and slightly over 30 inches.
-Joe