I have a few questions that I need answered. I already have the stillen downpipe on my car and if I wanted to buy headers what would be my best option? Since the cattman ones come with a downpipe would I just put the whole thing on or will they work with the Stillen downpipe. Also, is it true that their are hotshot 02's that can be converted for the 01'? If so, what is the easiest option?