I have receive PMs from a few memebers here asky me "why the JDM header will not fit" Here's the reason.
Left : stock header (size 28mm) vs Right :JDM aftermarket header (32mm)
The stock USDM header has a O2 bung to fit in the O2 sensor !
Where is the O2 bung on the JDM after market header 
The header will bolt up just fine but if you seriously want to fit any brand JDM header then you will need to drill a hole and weld on the O2 bung. You have to make sure the O2 sensor aligns properly because if the sensor stick too far in or out, it will affect the reading to the stock ECU.
Thanks
Ben