Generally speaking the aftermarket converters are smaller than the factory ones.
Sometimes it will be obvious like a bright shiny converter. Other tell tale signs are new exhaust pipes on both sides of it, adapters used to hold it in place, clamps when the factory would have welded it.
It's not the end of the world if you cut them out, it's just that you get spoiled on the $100 cats.
I say you grab a car trailer and have at it.