I was just reading about the new honda engines in the fit and jazz, http://asia.vtec.net/Engines/LSERIESG2/index.html and how the exhaust ports are part of the cylinder head, and the CAT is installed directly into the intergrated exhaust manifold... all to aid in reducing emmisions...
wow... these guys think about this sort of stuff a lot.
although a collapsed CAT could become expensive if you have to replace the whole head.