I'm by no means a H1RZ expert, but Wayne Toth has stated the mask was sculpted from a life cast of Tyler Mane. http://www.youtube.com/watch?v=xK1r6X-U4aA
Also there may have been as many as 3 Myers masks for Halloween 1, Tommy Lee wallace says they perfected the look by modifying several Kirk masks but the others were only ever used as back up or for stunt shots.
This cool photo from the Halloween '78 wrap party proves the other's existence: http://img855.imageshack.us/img855/6286 ... pparty.png
In the running for use as the mask in Halloween were, Richard Nixon, Emmett Kelley, Mr. Spock, and possibly Gerald Ford.
Also, Tommy Lee Wallace donned the mask for the closet scene in H1 because had made the prop closet door, and wanted it to break right the first time. Deborah Hill said she even wore the costume for the long shot of the shape watching Tommy across the street at night.