RE: Spacing the clutch nut
You should not have a spacer behind thee clutch nut. to stop the bell from sliding on the crank, put more spacers on the front where the screw goes into the crank. By putting a spacer there you move the clutch nut from its original spacing.
When you put the shoes on, the spring kinda centres the shoes. And with the nut moved, the shoes will move up also. They are probably only half on the pegs. This would be why they would break and the residue is not normal, that is probably from the shoes being moved closer to the bell and rubbing on the bell.