You will DEFINITELY have to pay a customs tax/. I have bought over $10,000 worth of parts from the US and paid it on the only item worth over $1000, the rest I have had split up and sent as seperate packages.
Bypass valve is the one. The reason they get you is not actually noise pollution. It is actually a breach of emissions controls. Vent to atmosphere blow-off valves vent oil vavour to the atmosphere, whilst by-pass or plumb-back blow-off valve recirculate the oil vapours back into the intake manifold for them to be burnt off through combustion.