The front of the catalytic converter section is shaped like a “Y” with each of the two legs attaching to an exhaust manifold, enabling three cylinders each. The front and rear exhaust manifold attachment points both use three studs and 15mm nuts each. To get them off is hard. One way that works is a wobbly extension and a long extension. I put the 15 mm socket on the fastener, with the long extension hanging down, threaded through the maze of bars underneath the car. Then, I attached a ratchet and used that to loosen the nut.
The back of the catalytic converter section attaches to the rear muffler section with two flanges, each of which uses a similar three-bolt pattern as at the exhaust manifold.
Even with the front and back fasteners removed, I found it impossible to remove the catalytic converter section unless I jacked the car high up in the air and also remove the front anti-sway bar. Even then, it took a lot of juggling and maneuvering.