My cat was stolen. I just found out there were two parts. Do you have the link where you bought the replacement?
I am a recent cat theft victim. 2005 Gen2 Prius. Those "2 parts" are likely to be the catalytic converter itself (this is actually 2 small catalytic converters welded together with a short pipe between them), plus the O2 sensor which screws into the pipe between the 2 cats. For my car I am getting the Walker aftermarket catalytic converter ($330) and a new O2 sensor from Rock Auto. This was recommended by my local exhaust system/muffler shop. I live in Illinois where aftermarket converters are legal. We don't have to undergo periodic smog tests in Illinois. If you go to Rock Auto and enter the year of your Prius it will show you pictures of what these parts look like.
Amazon sells a perfect fit cat for the G2 $110. Have one on my car as I sold my cat before it could get stolen.
Anybody sold your old cat to RRCats? They are giving me a quote of $550 for the 2cats in my 2007 Prius. But they will issue payment only after they process the CAT to extract precious metals.