You'll need a secondary O2s eliminator, they used to have them in the Summit racing catalog.
If those were advertised as catalytic converters, though, you need to report that company. Those are not cats, they are test pipes with shrouds. That sort of jackassery is what gives motorsports a bad name, and causes legislation like making it illegal to think about removing the cats.
FWIW, I had an F250 years back with a computer controlled carb and ignition, stock 351w, and a cat. It failed emissions horribly. I pulled that engine, disconnected the computer, and installed a very hotly built 300-6 with no cats and an old electronic ignition with mechanical and vacuum advance. Being an 84, they didn't do the mirror check to see if it had cats, just stuck the sniffer on and it passed amazingly well.
All a cat does is clean it up a bit, if the engine is running right in the first place they aren't needed.