Thanks for this. You may be aware that Australian heroes the Phantom Ranger, the Shadow and Sir Falcon have been published in translation in Brazil (as Cavaleiro Fantasma, do Sombra and Aguia Negra), with new stories being created in Portuguese. It seems likely that the link here is the Phantom: Frew, who originally published these three characters, holds the licence to republish and create Phantom stories, and (from what I can tell) the Brazilian company is also licenced to publish the Phantom, providing a channel for communications.
While Frew isn't involved with Devil Doone at all, KG Murray used to reprint DC, American Comic Group and Charlton publications (and probably more, I'm going from memory) in Australia. Perhaps this provided some opportunity to discuss reprinting some Australian content in Mexico.
Can't find much about Classicos del Terror online, so not sure if this is a one-off Devil Doone story in Spanish or if there was a series of such stories.