A 4-2-1 header will give more gains in the mid range and the 4-1 will give more gains in the top of the RPM range.

I am not sure if there was a JDM 4-2-1 ITR header or if the CTR header was 4-2-1. If the CTR header was 4-2-1 then I would make sure the engine you got wasa 1.8L and not the CTR 1.6L...and don't just look at the tranny stamp because they coulda swapped the tranny.