Hey guys i was wondering if headers for a US 99-00 Civic SI will fit on my jdm B16A? PLease let me know, very important, thanks

 

Im pretty sure they will fit. the only trouble is length. if it doesnt fit, what i would do is go to a muffler shop and buy a high-flow cat and have then weld it to fit. they will just need to make the cat longer or shorter than stock. just make sure they weld flanges on. some will want to cut off the flanges and weld it all straight together.