the 300zx has a tilted radiator, right?
if that is so, I would NOT mount the fan on the back of the radiator support, unless you are building some kind of shroud that will direct all the suction of the fan to the radiator.
I had a taurus 2 speed electric fan setup pusher style on my car, and the temp gauge would get hotter than I liked. I checked out the operation of it, and since I didn't have it flush mounted to the radiator, alot of the air was spilling out the sides, and not being forced through the radiator.
even a small electric fan will do if mounted flush with the radiator, and with the right control device.
good luck
-oliver