302 harmonic balancer identification

[Limey57]

When the rotating assembly was balanced, quite a lot had to be machined off the late model AOD flex plate so I suspect the HB is a 28 oz, but can anyone confirm? Is this a 28 or 50 oz balancer?  On fitting it, there is wear in the keyway so I need to replace it.  The engine is a late '79 block, AOD & flex plate are from a late 80's car.  Photos of it below: