I wish you all the best with your research. I know you have made enquiries with more US centric forums, so hopefully you will get some more positive responses from people who actually built and flew the Electra. It was certainly an interesting, if tragic, time in the development of modern aviation.
I came across some fascinating footage on YouTube from those times. It is amazing how the aircraft manufacturers of the time were allowed to play down the seriousness of the problems they faced. Severe structurally destructive vibrations in the airframe became a program to reduce cabin noise levels and increase passenger comfort after the marketing departments had done their job.
Simply incredible!