[Christ]

Re: The exhaust.

If the XFi doesn't have one, nothing to worry about (except if you need to go through visual emissions, but that's a different story altogether).

If the XFi does have one, best to use it's OE location (close as possible). The Civic's stock location is in one of three places: In one pipe of the exhaust manifold (not common); in the plenum of the exhaust manifold (HF/Std models); or at the union of all 4 pipes in the long-runner manifold, right above the down-pipe flange.

The Honda's catalytic converter should be OK for the 3 cylinder engine, so long as it has the same inputs (AIR, etc..).