Internal or External Balanced Harmonic Damper?
Yea, It looks like someone tried to duplicate an externally a 360 balancer using a neutral balancer. Notice that weight is taken out on the keyway side also.
Pic is of a later model 360 where the factory removed weight. The original 360 version had a counterweight cast into it opposite of the keyway. I guess it as a manufacturing and material cost saving measure to take weight out instead of adding it. (Kinda like B&M did with their externally balanced flexplates.)
If everything internally is OEM and not lightened, an OEM 360 (non-Magnum) balancer should work. But you don't know if anything was changed inside.