Check out the soundtracks in the photos - they all look like glorious mono… except the first one that looks to be stereo! We might end up with quite a funky soundtrack. 😄
Those look like stereo optical tracks to me - two stripes. They probably look like similar channels in those sections because they’re dialogue scenes, i.e. common information to be directed to the centre by the decoder.
I’m certainly not aware of the existence of a mono Alien mix, anyway…