I'm not 100% versed on G35s/350z but from what I've seen, they have a lot of room, more than S14s. Those are fucking pathetic. Have him look into rimtuck.com and get an idea in there. Remember tho, you lower those cars, its not just a matter of coilovers, he'd need to upgrade alot more than that if he wants his alignment to be back to spec.
http://www.rimtuck.com/search/thumbn...odel=G35+coupe