So, I was a bit confused when I saw Clive Curtis said he worked on Alien on his website as a stuntman, since the only stuntmen that worked on Alien I knew of was Eddie Powell and Roy Scammell, so I sent him an email, thinking I wouldn't receive a response, but this was in my inbox today:
The end sequence of the film was to be a big fight scene between The Alien and Yaphet Kotto, whom I doubled. However, after shooting the sequence, the powers to be decided not to use it for fear of upstaging the image of the alien bursting from the person’s chest, thus it was not used.
Regards,
Clive Curtis