Ah we had actually updated the film’s entry in the database but didn’t let y’all know about it 
Hills is best known for the hilarious Brit beatnik exploitation film, Beat Girl (1959), in which she appeared as the titular character at the age of 15 alongside Ollie Reed, Christopher Lee, Shirley Anne Field, Adam Faith, Nigel Green and other well-known figures. She also appeared as the female lead in a Hammer horror, Demons of the Mind, filmed in 1971. She was better known as a singer and didn’t have much of a film career.
Her Wikipedia entry says she gave up films in 1972 and went to New York and then lists this film and The Killer Wore Gloves (1974), another Juan Bosch films, as being made by her afterwards.
Having checked the Wikipedia reference for the comment that Hills gave up films in 1972 it is a long interview with Hills in 2017 I think and she doesn’t state that she gave up films in 1972 (no date given but she wasn’t asked the question).
The Killer Wore Gloves was signed off by the Italian censors in July 1974 and 10 Killers from Afar in May 1974 (and was released in June 1974). The other Steffen/Bosch western was signed off in June 1972. All 3 films were Sp/It co-productions with the same companies. Grimaldi’s PEA was the Italian company involved. I do find it hard to believe that PEA would sit on this movie for 2 years before releasing it, especially as they had a later giallo deal with the Spanish company (unless they sat on the giallo as well). Possibly some scenes were taken from the previous film? All 3 films have same director, DoP and composer but not quite the same casts or production designers. I’ll have to watch this at some point.
Steffen’s character is called ‘Dallas’ in the Italian censor notes also.