It amazes me the weird, retarded solutions to having an exhaust that people dream up. Sounds like the guy really wanted a 2.5" header, but then used the stock exhaust pipes welded up to an aftermarket muffler. That's just dumb.

You could get a universal Carsound cat and have a muffler shop fab it up to work with the current system. It'd pass no problem as long as there are no leaks, but you would still have the same screwy setup which you dumped more money into.

Part of me feels like you should junk the whole exhaust setup due to high levels of crappyness and start over; although if that's not something which is affordable to you then I guess you're stuck with just making the current wacky setup legal.