CJS a you are correct that raceways with conductors larger than 4 AWG need a bushing that is 300.4(F) in the 2002.
However if you go to Article 352 you will find 352.46 requires a plastic bushing on all PVC regardless of wire size.
The bonding of a metal sweep in a PVC raceway is not needed if it is below ground. (250.80 Exception)
If it is exposed but goes into a metal enclosure with two lock nuts it will not need bonding bushings unless it has service conductors in it or is using concentric KOs not listed for the purpose and is has conductors operating over 250 volts to ground. (250.97)
