It goes all the way thru. It's purpose is to dampen the harmonics (vibration) of the engine, hence it's name "harmonic balancer".
There are aftermarket dampers available, or you can have yours rebuilt at a place like http://www.damperdoctor.com/ There are others out there.
I doubt you can do it yourself, since the keyway on the inner needs to be precisely aligned with the timing mark on the outer. If it isn't, you won't be able to time the engine correctly.
Since the AMC 360 is an externally balanced motor, the harmonic balancer and flywheel/flexplate are where the balancing is done. A replacement balancer MUST come from a 360 engine.
Bob
tufcj
