There many different part numbers, because they come in different colors, to match the color of the bumper and body.
Microfiche sucks, get the Nissan parts program called FAST. It is a windows based program that is very user friendly and has many search engines. Not only does it covers the Z31, it covers every Datsun/Nissan model made.
E-mail me with the VIN of your car and I will reply with the correct part numbers.