Ok, just wanted to be sure, the reason I ask is because I sometimes see these codes "falsely" or store becuase the car was not running right such as if you just had a tank of bad fuel that caused misfires and engine flooding.
So if the car has been running fine and no recent history other then the stand alone 420/430 codes then this is an isolated issue.
First let me say that I am sorry but you wasted a lot of $$$ on sensors, when a 420 or 430 code stores and no other codes then this means that the sensors in the exhaust ARE working normally and the catalyst is not, I commonly see this costly mistake in my shop.
Secondly this is not a "known" issue on your car.
There were a few updates to the 4 cylinder model camry in this year where the computer monitor programming had to be altered and the converter replaced to prevent repeat 420 codes, if you have found anything online about "common" issues with these codes on your year camry just be aware that this does NOT apply to your car as it is a v6.
As far as converters go...you asked how to verify failure, the o2 and air fuel ratio sensors have already done that for you. The converter on teh manifold is more of a "pre-cat" then a true converter, the three way catalytic converter in the forward exhaust center pipe will need to be replaced here and the car then retested.