Hi.
Whirl mode ending in fatal impact was well described in the two accidents I reviewed. My experience as pax in the Electra involved seated portside abeam the engines and witnessing it first hand. It is impressive. In my case the aircraft was short, and full power added whilst level at one hundred feet. The two port engines were wobbling and the aircraft was shaking so bad the passengers were alarmed. There were a couple of screams as I recall.
In the takeoff roll, at rotation, the stresses are at max on the mounts, and whirl mode is one loose motor mount away.
Have you the logs and maintenance records? I would consider whirl mode, especially as one engine left the airframe before the others?