the 2 cats were for a 2 stage emissions systems - the first one is a quick light off cat to start working quickly , the second one is for after the motor warms up. Nowadays, you only need the 2nd cat to meet emissions, so the first one could be pulled from the manifold, and they wouldn't be the wiser. BTW, that cat is the old style cats that bring good money at the scrap yard - don't just toss it.