Resonating vibration

Are the 360LA and Magnum dampers the same? I thought some 360LA's were internally balanced?

No, the 360 LA uses more offset weight as the stock LA pistons are heavier than the Magnum pistons. All 360 Mopar engines whether LA or Magnum were externally balanced from the factory.

All other SBM engines (273, 318, 340) were internally balanced except for the 1973 340 engines that had cast crankshafts.