No, but the final script was pieced together after shooting, and whatever was different substantially [ie, Ash's speech or cut content] was revised. The shooting script was dated July '78, and features different lines for different speakers, etc. After shooting, Giler and Hill revised the script to reflect whatever they had seen onset [mostly Giler, as Hill didn't step foot in England]. This script still doesn't reflect the final movie, as you say, because the film was still being cut. As it stands, it's the closest to the final film, though it differs.
As for O'Bannon's script, as said, the content is all there: from ship waking its crew due to an alien SOS, to motion tracking devices and a flamethrower weapon, from hunting the Alien with electrical prods only to get jumped by the full grown creature, an airduct sequence, the Alien jumping two of the crewmen whilst another can only listen, an airlock sequence [that found itself in Giler and Hill's script but not in the movie], Broussard/Kane's body drifting outside the ship [also scrapped in the final movie, though it was storyboarded by Ridley Scott], a self-detonation countdown that is unable to be aborted despite an attempt, the lone survivor dashing through the halls of the imminently exploding ship whilst clutching a flamethrower, saving the cat and taking the lifeboat, the Alien stowing away on the lifeboat, the lone survivor hides in a locker and pulls on a space suit as the Alien is distracted by the cat, the hero shoots the Alien with a speargun and ejects the Alien, which grabs onto his foot, the hero managing to shake off the Alien's grasp and trapping it outside, igniting the Alien with the jets, and then finally, cryo-sleep with the cat.
^ That is why O'Bannon got his credit, and why Giler and Hill really writing Alien isn't true. None of those things -the story itself- were theirs. They simply refined something they were given. I've said it before: collaboration.
Re; disagreeing. That's fine, because we're wildly off-topic. Let's return to it.
