A pressure plate and clutch disk are not part of the engine and as a result would be zero/neutral balanced by the manufacture. When removing a used unit and reinstalling it is marked to simply allow for wear matching.
The flywheel on the other hand can relate to the engine. If the engine is internal balanced the flywheel should be neutral balanced. If the engine is external balanced then builders will balance the flywheel to the engine.
If you are building to performance engine levels then every thing is balanced as a unit for high RPM performance.
