Ouch. The crack in the clutch disk does not look good. That will need to be replaced. The metal in the gearbox is hard to say. Look at all the bearing cages to see if any are missing. Could also be pieces from the parking brake on a super. Looks fairly clean otherwise. Dandy Dave!
Re the fragments you found in your gearbox, they look like a disintegrated wear plate from the transmission brake. The dowel in your photo, one of two, holds the interleaved stationary plates in position and it looks like it has got very hot. Highly likely that the brake has been left on at some point - a not uncommon occurrence. The photo below shows the two types of plate interleaved. New plates are available. As you've got the gearbox apart, it's worth fixing.
Best
Adrian
Oops! Just looked at your photos again. You haven't got your gearbox apart! Still, where you are now, it's not a big job. Remove the primary gearbox and you're there. I'd recommend fixing it.
Best
Adrian