RE: Spacing the clutch nut
Well 1. Your bearings, shoes, and clutch bell are all pretty shot get some new ones. 2. That grime looks to be standard grime that is formed when nitro and oil mix with dirt. It looks like you just need to clean that car more often, and set your gear mesh better because that clutch bell shouldn't wear out like that for a long time. Also when shimming a clutch bell you put spacers on the other side of the clutch nut as well as in front of the clutch bell if needed, not behind the nut.