If you want to install 6x9's in the parcel shelf on an R33, make sure you have a day spare. it took me the best part of a day to get them in there, they need some hefty spacers. i've had 2 headunits stolen, so i know my way around that area of the skyline. There's a headunit install guide on this site somewhere, i think in the maintenance section. give it a shot, it worked for me, 3 times now. door speakers are easy to get at too, just have to unhook the interior door panels and they're right there. some people have put 6x9's in the side of the passenger walls, just above the armrest in the backseat, but that requires some cutting, and i wasn't confident i could do that nicely.