Help identify metal in 1965 SM420 manual transmission

[markbritt]

I have a 1965 C10 that is a father and son project. We trailered this back from South Dakota and only ran it about a mile before we decided to do a frame off.

Today I drained the SM420 (oil was black) and opened the PTO port. On top of the magnet was a ball of metal. If it were just flakes, I would not be too concerned, but there are pieces here. All the pieces are thin metal - like a washer? I took the cover off and inspected every gear - no teeth missing nor are they chaffed or gouged. The transmission functions in all 4 forward and single reverse gears.

I am asking what this could be from? I am concerned on the two pieces in the lower left - they are heavy duty, so they were not deformed. Could this be some piece that goes between the gears on the main shaft? Again the transmission seems to shift just fine and there appears to be no slop in the gears. Any help would be appreciated.