The most predominant thing in the scripts and treatments is the "death star" or space fortress, and it is no wonder that it is used twice in the films. Lucas just couldn't come up with another "big idea" to keep the movies going.
Essentially, they are all the same movie, ANH. So, there really was no super-detailed outline. Most of it is just a flotsam of ideas that seem to conveniently fall into place when Lucas needs, whether they really work or not.
There are several versions of Han Solo, and there are several versions of Ben Kenobi and Darth Vader. Han Solo's description in one script describes him as large reptilian, and he and a Jedi character embrace when they meet. Sound familiar?
There are scenes where these Wookies (called Jawas in one script) have a battle with the Imperial-like characters, which resembles, of course, the battle on Endor. There is also a "Count" character, a corrupt senator. Vader is a grand moff-like character in one. There is a scene where an "agent of Lettow" (Sith lord) suddenly turns on the Empire to help a Jedi (no true motivation sited).
So, Lucas just kept switching the pieces around until something shaped up.
Just for fun, I've been illustrating one of the scripts. I'll let you know when it's all done.
