I posted a question moments ago regarding finding someone to install 18mm bungs on my stock 2014 catless exhaust. Is there any reason I couldn't use a 2009 header pipe that already has 18mm bungs on it with a Target Tune wide band closed loop system?
Just ensure the 18mm bungs are up close to the jugs... wideband O2's should be installed up close to the jugs to get an accurate reading by design. If they are in the stock location, as your current narrowband O2's, I am not certain you will get an accurate reading that far away from the jugs.
Something to research before you dive in..... as I am not 100% sure on how they will read since every wideband O2 I have seen installed ( by design ) is on the down tube as close as possible to the jugs.