$:£ rate is good for shipping, i just bought a merge collector for my turbo mani and even with £40 tax it was better than I could have done here.
find a mate in the US! that is the answer
As for KO4's I know cars that have BAM blocks from TT's running over 300 on a KO4 (ok I know it is not the longtudinal model) but it is possible, thing is it is on the absolute limit of boost and EGT.
you will need bigger injectors anyway, regardless.
AFAIK TT 225bhp injectors are different to yours, get some 440's to be sure, £100 for a good second hand set