i think there is a difference underneath between USDM and UK.
i think a few people have bought HKS copies (not true duals) and had to have them modified slightly to go round the diff (i think)
i have the invidia which is a yank system and it fitted fine. so the others should be fine. i think true duals are easier as the path they take tends to miss all the vitals
HKS is a true dual
Some exhausts will interfere with the cover on the diff, US cars don't have the cover
+1 I've got HKS replica on mine and it fitted fine (JDM). Didn't fit on nurrish's UK car.