P0420 code

I have a 96 grand marquis and it has two catalytic converters with upstream and downstream o2 sensors. Since the check engine light came on I went out and bought a code reader. It tells me that cataylst system efficeince below threshold bank one. This cat converter is only about a year old. I had both replaced and I recently replaced all the o2 sensors with bosch. It made quite a performance change for the better. Also had the maf replaced too. also what a difference. on the hwy I get about 27 to 29 mpg. outstanding. however on hard excelleration I have alot of diesling.

Now back to my question. My repair book does not indicate which side bank one and two are. How do I determine the drivers side sensors from the passenger side sensors? And then how do I determine which sensor is bad? or is it the cat converter that is faulty?

This link should help you out.
P0420 (http://www.obd-codes.com/trouble_codes/generic/p0420-catalyst-efficiency-below-threshold-bank-1.php)

I think bank 1 should be the one with cylinder 1. Not positive but someone will know for sure.

Bank1 is the passenger side I just had the 02 sensor changed in mine but thats what the mechanic told me

code 420 is for left bank is this not the driver's side