In all the photos, they are labelled as follows:
A ) Bank 1 Sensor 2
B ) Bank 1 Sensor 1
C ) Bank 2 Sensor 1
D ) Bank 2 Sensor 2
Bank 1 always refers to the bank of cylinders with no 1 cylinder in it. On the GS430, looking from the front of the car, cylinder 1 is the first pot on the right hand side. That is the nearside (passenger side) in the UK, but would be offside (drivers side) in the US. All you need to remember is that the engine layout is exactly the same in any country, so it will always be on the right side of the viewed from the front. Once you are on the correct bank, Sensor 1 is precat, so in the down pipe very near the engine. Sensor 2 is post cat, so around the front seating/footwell area. My advise, when buying sensors is to ALWAYS order them as bank x sensor y, never as nearside or offside. That way, it makes no difference if you are sourcing them in the UK or the States, you will always get the right one.
If you have a code reader, or get the codes read, you may get any of the following codes relating to the faulty sensor concerned:
A ) P0136, P0137, P0138, P0139, P0140, P0141
B ) P0130, P0131, P0132, P0133, P0134, P0135
C ) P0150, P0151, P0152, P0153, P0154, P0155
D ) P0156, P0157, P0158, P0159, P0160, P0161
Refer to the following pics to help further.
I hope these help someone a little if they need to tackle the job.