In the original Japanese version of this film Allegra's name was Kiki, and Queen Ariauna's name was Grendel.
The automobile that Jack and friends drive is a Ford Model T.
This film is an updated adaptation of the poem "Beowulf", not of "Jack and the Beanstalk" (nor "Jack the Giant Killer". The common mistake likely derives from confusion with the contemporaneous anime feature Jack and the Beanstalk (1974).
Was the first anime to win Best Score at the Mainichi Film Awards.