While ATI have the name, BHJ Dynamics in California also do some excellent harmonic balancers. A quick look on their website didn't show up a balancer for the 360 but I'm sure they do one.
The harmonic balancer's job is quite complex. This 'White Paper' from BHJ gives a lot of information about the many variables and different types of balancers used in all types of engines:
Damper Technology White Paper : HarmonicDampers.com by BHJ Dynamics, Performance Harmonic Dampers, Harmonic Balancers and Specialty Crankshaft Vibration Dampers