Yes, it seems a bit different from the LS430.
I looked it up in the Toyota/Lexus catalogue and indeed it seems that you would have to replace the whole assy.
The actual air flow meter sensor is quite small.
I made a photo of the interior of the sensor in my LS430 (which is in the air stream):
You could try cleaning it with a spray can of MAF cleaner, if you have not done that already.
Sorry I can't be of more help to you.
Jac