you may want to check out the integrated o2 housing/down pipe from MAP performance. Rather than buy a separate o2 housing and dp, you get both in one piece.

 

i think im going to get either the ultimate racing o2/dp in one for 369, or the atp transformable 02/dp in one for 400. right now im leaning towards the ultimate racing but still shopping around for better prices. im also getting the greddy spectrum elite exhaust to go with this. gonna sound nicee

 

I'm in the same boat but debating whether the O2 housing is worthwhile. I have CBE, downpipe and HFC.

Some people say that your exhaust is only as powerful and your narrowest part, so if you have a 2.5' CBE with 3' tbe/o2 housing, it's as if the whole exhaust were 2.5'. I think this is an overstatement but there is some truth to it.