1991 Toyota Celica catalytic converter

I have a 1991 Toyota celica gt with a 2.2L 5a-fe engine. The catalytic converter on this model is very strange. It's actually called a manifold converter. It is attached directly to the exhaust manifold. On the manifold side the opening of the cat is about 3 inches in diameter, on the exhaust side it is only about 1 inch in diameter. Hypothetically, if i were to gut the cat and reattach it would I be susceptible to any problems from the open cavity in the cat? I have never seen a cat like this and am worried that a vortex might develop inside and cause the car to backfire or fry the valves.