I saw SW in June 77. I was 17, and in Logan Utah for a summer math program with 50 other high school kids. We all saw it as a group when it hit the local theater. To get to the theater, we had to walk from the dorm through a cemetary. Saw it two more times that week, walking through the cemetary each night with a group of friends.
A few weeks later, when I went back to California (Greyhound bus each way), I dragged my parents to the theater to see it.
Since then, I've deduced that the Logan showing was 35mm mono mix, and the later showing in CA was probably 70mm.