Direct Fit Catalytic Converter

Is there such a thing? All my research points to no. But I have noticed that certain applications to Cadillacs are similar in apperance. Namely a 96 Deville. See Here (http://www.autopartswarehouse.com/catalytic/cadillac~deville~1996~parts.html) Im curious to know if the rectangular flange is the same pattern or not. The resonator/muffler behind the cat may need to be omitted but no real big loss. Anyone tried this or maybe have more info about replacing the factory converter?

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