Very intriguing that you saw this film in 1987. Do you mean this particular piece of film, which, to my understanding, was made by Roger Judd in the 1970s? Where did you come across the film you saw? What is your opinion as to the similarity of Mindy's swing to that of Richard Wax?
I don't think of Mindy's shoulder turn as being particularly limited and it would seem that to achieve full "stretching" of the "transmission" muscles between the legs and hands, the shoulders should turn as fully as the golfer is capable. However, Blake certainly did not turn his shoulders to the extent common among modern professional golfers. However, his backswing does look short--it's almost like a 3/4 swing in terms of how far back he took the club. In an exchange I once had with Roger he told me that he and Mindy deliberately tried to shorten their backswings but still attain full power. I think one could attain full power only with a full shoulder turn.
As to the use of the trail arm, when I hit my best reflex swing shots, the trail arm feels as if it is simply an integral part of the "dragging" action initiated by the legs. There seems to be no overt action by the trail arm--it's just going along for the ride until physics intervenes and "releases" in accordance with conservation of angular momentum. I cannot be certain that my initial leg action provides the power (solely Mindy would say) or whether the leg action only "triggers" action by my upper body.
My big problem with Blake's swing has mainly been mastering the longer clubs, ie, anything longer than a five iron doesn't work as well for me. Of course, to some extent most amateurs have greater difficulty with longer clubs. Forum member Tom tried the Blake swing in the 1970s and reports that he had success only with shorter clubs. Have you experienced this phenomenon? I seem to remember that, in Dallas, you were hitting some long clubs, including woods, pretty straight and powerfully. Jim