"Iron Hans" ("Iron John"?) in Grimm (1785-1863 & 1786-1859) contains the same basic plot as that of "Guerrino and the Savage Man:" the protagonist is helped in his quest(s) by a wild or savage man he sets free.
The plot in Straparola's "Ancilotto" is followed closely, with some differing details, in "The Dancing Water, the Singing Apple, and the Speaking Bird" as found in Joseph Jacobs's collection of 1916: to prevent a king from meeting with his children, they're sent on near-impossible quests.