Removing/replacing that portion still doesn't take care of the problem with the SLR headers displacing the primary cats.
Even if the part shown above is actually a secondary cat on the California/etc. 2000 and all 2001+ models, removing them would be inconsequential, the engine and emissions system would be oblivious.
The rear 02 sensors that go into them are also useless, they're only there to detect if the primary cats fail. You can buy "dummy" rear 02 sensors to connect in place of the ones that go into the part shown above and not have to worry about ensuring whatever replaces that portion of the exhaust has bungs for the rear 02 sensors.

Anyway, we're no closer to making an emissions-compliant installation of the SLR headers happen...

Brent