I brought a tial wastegate from states but seller stated the declaration as a 'gift' so got away with paying no import tax but have been caught many times before. a small box with a air filter kit in cost me over £30 in charges when it arrived in the uk
your limits wont be on the engine as it is forged, your limit will be on the TD04 as it wont take much more than 1.3/1.4 bar of boost but its already been said get some decent management should be your first port of call buddy