Magnum Harmonic Balancers

My understanding is that a 273, 318, 340 and 5.2 magnum all can use a common balancer since they are internally balanced. Can anyone comfirm this?

Sort of. All internal balanced small blocks can use the same neutral balanced dampener.
The external balanced 340s must use a specific 340 external balanced dampener.
All LA 360s from the factory use a specific external balanced dampener.
All years of 5.9 Magnum from the factory use their own Magnum external balanced dampener.
All non-factory small blocks are handled individually, but when internally balanced, can use the basic neutral balanced dampener.
All applications still need appropriate flex plates.
The Professional Products harmonic balancer, or dampener, includes bolt-on weights so it can be set up for any of these applications by installing the application specific weight.