Did you check which version of the calipers you have??
The 300Z had 2 versions - one takes a 30mm rotor, and one takes a 26mm rotor. With the 30mm rotor in a 26mm caliper, the pads may not be able to push back far enough to clear.
joe
http://www.negative-camber.org/jam1491992 240SX Racecar1998 240SX Track Queen