Replace the upstream O2 sensors, not the downstream ones. Leave the downstream ones alone.
To keep the P0430 code from coming back, you want the upstream O2 sensor to switch faster than the downstream sensor.
O2 sensors start switching slower as they age, so it would stand to reason that replacing the upstream O2 sensors and leaving the downstream ones alone might change the upstream/downstream switch ratio enough to make the P0430 code go away. Might being the key word. I can't promise anything.
Also, I talked with my mechanic about how the B12 Chemtoool seemingly fixed the cat, and he mentioned that carburetor cleaner heats the cats up, which might be the sort of "kick start" they need to start working efficiently.
So before you replace those cats, might I suggest spraying some B12 Chemtool or other carb/throttle body cleaner into the intake with the engine running? When I did mine I sprayed the cleaner for 10 seconds while revving the engine, let the engine idle for 10 seconds without spraying any cleaner in, and did this until I'd used about half of a 16oz can.
If you use B12 Chemtool, it's got a powerful enough stream that you can spray it in from a foot away. Most of the throttle body cleaners have a weak stream and it's hard to spray them in effectively without completely removing the air duct.