It is illegal in Victoria to cut a hole under the battery tray.
it sucks, and it doesnt make sense why to me, but thems the rules.
i dont understand, because as you said, 260RS's have holes there, GTR's have holes there....
stupid vic roads.
few skyline guys down here got done for it, i was lucky i never got pulled over.
you can get an engineers cert. for it, but is it really worth the hassle?
if i ever choose to go for a FMIC, i will buy a cooler, and get custom pipes made up like what alex did. or get a blitz/greddy/ARC cooler kit.
hope that helps