i see where your coming from, if your using a xf throttle body, its easy to get your hands on a bigger diameter air ducting, but a larger AFM is a bit harder to find, look into it mate, and let me know as i'd like to get my hands on a larger one that is compatible.
The 3.0l Nissan Patrol uses the RB30 still and the air intake side might be bigger, you might be able to use one out of a patrol then, look into it mate.
I wouldn't worry too much, Unless you could pull it apart and put it in a new piece of pipe. But i dont think it'd make a difference at all. Especially with stock t/b. And stock inlet. And stock engine.