So long as you get either the Random Tech or CATCO you will get a CARB approved replacement. It is not necessary to use the stock unit-unless you really want to.
What I mean by OBD-II is the computer requires that there be an O2 sensor both before and after the CAT. ALL 97+ Preludes have this from the factory. The laws of most states and the Federal Gov't. require that the emissions system be kept as supplied by the car maker as to design.
You can check with a local muffler shop such as Meineke for the CATCO convertor. They did the one on my race car and it works just fine for the sniffer.