Thanks megan, for the links. I am trying to suss my misunderstanding of Whirl Mode. I think I stated the phenomenon is common, and not unique to the Electra.
The concentration of power/mass locally (well forward of the wing) cannot be dismissed. The propellors are heavy, and have an unusually long moment arm related to the forward wing spar. It provides an extreme and asymmetric increase in power translated during whirl, relative to other installations. My experience with Whirl Mode occurred on short Final, as pilot selected full power to make up for an undershoot. The articulation of the nacelle was extreme, I promise you it was profoundly distressing to this passenger.