Well, there are a few possibilities.
1. That is part of the rear planetary torrington bearing.
2. The rebuilder did a shoddy job and those parts are from before the rebuild.
3. Might be pieces of the forward sprag, but i think they are too small.
Man, i should have said drop the pan before you went this far...
Well, if it is bad, its bad. If it was me, id shoot the moon. Put the case back in, and see if it still makes noise. That's what I would do.
Hell, when the 2-4 band in my Silverado was bad i was in denial and welded a booger on the pin tip to get me some more clamp distance for a month lol