I'm no expert but for a job that requires so much time and effort, I wouldn't bother with cheap brands you've never heard of. Exedy probably made your original 'Nissan' clutch so I'd go for that one :) (or Sachs or Fuchs :D) .
Diesels are what's called 'excess air' engines ie there's always more air in the cylinder than is needed for the diesel to burn. This makes the combustion very hot and generates nitrous oxides. Adding some exhaust gas into the cylinder replaces some of the air and lowers the combustion...