Ralph McQuarrie’s helmet for Han was definitely inspired by Alex Raymond’s Flash Gordon, as he himself said. You may be right about the similarity being too obvious for film, though.
The August 1975 third-draft script for SW states pretty clearly that Leia is bloody and bruised from Vader’s torture, so much so that she remains unconscious until the garbage compactor scene and Chewbacca carries her around.
The idea of a barebreasted Leia isn’t explicitly mentioned in the third draft – but then the idea of the second draft’s Luke Starkiller being turned into a female protagonist also didn’t make script form, and Ralph McQuarrie made half a dozen color drawings of girl-Luke. And of course THX 1138 had onscreen nudity.
In the second Ralph McQuarrie storyboard storyboard in my first post, Leia appears to be covering her bare chest with her right arm, and holding a blaster in her left hand:
A detail from another McQuarrie drawing of Leia and the torture robot shows that her dress has fallen down to expose her left breast:
John Mollo in the Star Wars Costumes book states that Leia was going to have a “Tarzan-like” outfit at one point. Of course Johnny Weissmuller wore just a loincloth, but earlier Tarzan movies had the Jungle King wear a garment with one shoulder strap, so that he only exposed half his chest.
Either way, it’s very likely that GL wanted Leia doing a French Revolution Liberty Leading the People cosplay:
This goes back to the 1974 rough draft, which describes Leia as “half-naked” after being assaulted by the Ureallian trappers (of the same species as green-skinned swamp thing" Han Solo).
It seems that GL abandoned the idea of on-screen nudity around the January 1976 fourth draft, which is right around the time he was becoming desperately afraid that his film was going to flop at the box office. Making sure the film got a PG rating instead of an R was one way to maximize profits and increase the chances of him being able to make SW sequels. Of course in the event he didn’t need to worry.