My sources are those which are available to every man: the books and scripts of Star Wars themselves. (For ease of reference: Virtually all of the early draft scripts of SW are easily available here.)
One has merely to read between the lines to figure it out.
For instance, look closely at Ralph McQuarrie's thumbnail sketches for the famous Death Star chasm swing painting.
Having done so, it becomes clear (to those with open eyes) that Leia is wearing only a "Tarzan-style" loincloth... an idea which is also mentioned, in passing, in the recent Star Wars Costumes book.
In the sketch below, for instance, Leia is evidently using one arm to cover her bare chest.
Likewise, it is clear from the text of the 1975 third draft that a) Leia was to be "bloody and mutilated" as a result of Imperial torture, and b) Ben Kenobi was indisputably a cyborg himself, like Luke in ROTJ.
(The Darth Vader of 1975, on the other hand, evidently had no problems taking off his mask to drink a glass of water.)
Even in the later films, darker implications remained. According to The Making of Return of the Jedi, for instance, Lawrence Kasdan's first draft of the script contained dialogue revealing that Leia suffered "a fate worse than death" (a euphemism for rape) at Jabba's hands.
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Next, from the evidence presented before our eyes, we can extrapolate and hypothesize.
The 1974 rough draft, in stark contrast to the final film, appears to describe a Star Wars with bright white Imperial hallways and black Stormtrooper armor.... extremely reminiscent visually of Lucas' earlier film THX 1138.
That film, of course, featured on-screen nudity. (Which, I should point out, did not affect the PG rating in 1971, but merited an R on re-release in 2004. Times change!)
And the THX 1138 novelization is indisputably more violent than the film. The heroine LUH has a scarlet brand on her face, marking her as a product of illegal sexual activity; and she suffers some of the very tortures I have detailed in the posts above.
But that Lucas approved some of the novelization's content I cannot doubt.
In the 1971 original cut of THX 1138, THX confronts a pack of angry mutated dwarfs during his escape to the surface. But in the 2004 re-release, the dwarfs were digitally replaced with CGI ape-monsters--an idea which first appeared in the original novelization.
Turning back to the original ideas for Star Wars: if it resembled Lucas' earlier work in one way, might it not in others?
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I do not fault you for questioning my logic here. Far from it! Questioning leads to wisdom, after all.
But in order to reconstruct GL's true intentions, one must move onward from reasoning, and acquire for oneself the most fundamental capacity of a filmmaker.
Imagination.
Thus, when I am asked: Is this story real, or did you make it up? I can only say: Both.
Or better yet: It doesn't matter.
But... reasoning still has an important place.
I have heard it said (by a moderator on TheForce.net, no less) that even JW Rinzler did not have access to GL's full set of working notes when writing the Making Of books.
What cannot be seen, therefore, has to be imagined.
This tale may be a flawed reconstruction of a notional Star Wars, one that exists only in handwritten drafts on yellowed sheets of paper... yet, I am in little doubt, it gets at the essential truth of the story.
I myself would very much like to see those "secret notes" for myself some day, and see how close I have come to the mark.
Until then, I can only keep guessing.