Ringo, Big River Lawman by James Zee

Why Ringo?

For some reason, KG Murray chose to publish "Ringo" rather than "Gringo", a change that reflects the reworking of the foreign Johnny Galaxia title into the anglicised Johnny Galaxy.

The Treasure
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The series was almost certainly renamed in Australia, specifically for Murray's editions. The original Gringo title was consistently used in other countries and even in later Australian printings by Gredown.11Episodes of Gringo were also printed by Australia's Gredown Pty Ltd in the late 1970s. Thanks to Kevin, Spiros and...  

El Secreto de los Pantanos
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It can't have been a casual choice as it led to consistent additional editorial work for each issue. While the translation and English presentation is professionally done overall (and probably provided to KG Murray in that form), most of the reprints have been noticeably altered with the "G" cropped, blacked out or whited over.

From a marketing perspective, Murray may have decided that the title "Ringo" had broad reader recognition as a western comic. Numerous fictionalised versions of the life of Johnny Ringo, including Wyatt Earp, Doc Holliday, the OK Corral and Tombstone Arizona, have effectively associate him with the traditional western archetype. The hit theme song of the long-running TV series Bonanza (1959-1973) was also called Ringo, firmly embedding the association in the Australian consciousness.22Kevin Patrick suggests a direct link to "Ringo" titled spaghetti western films that cashed in on Sergio Leone's success, such...  

KG Murray may also have avoided "Gringo" because it has a strong pejorative connotation in English, despite its more neutral meaning as a white American for many Spanish speakers.

Above all, it is clear that the company was not yet ready to abandon its long-standing tradition of disguising the international origins of its material.33As recently as 1968, Murray was still deleting "of America" from its Justice League of America reprints....  

References

Episodes of Gringo were also printed by Australia's Gredown Pty Ltd in the late 1970s. Thanks to Kevin, Spiros and Mark for identfying some of these stories. See also Kevin's Comics Down Under: The Spanish Connection. Gredown also reprinted Carlos Giménez's Delta 99 in Australia.
Kevin Patrick suggests a direct link to "Ringo" titled spaghetti western films that cashed in on Sergio Leone's success, such as Pistol for Ringo (1965) and The Return of Ringo (1965). These could also have been doing the local cinema/drive-in circuit around 1966-67.
As recently as 1968, Murray was still deleting "of America" from its Justice League of America reprints.