1BadTitan...
Here is a wheel calculator to figure out what you need.
Going with that large of a wheel diameter, I am potentially affraid that the only tires you are going to find are street tires and not off-road varieties.
Plug the 'current numbers' in the first column and then your guesstimate numbers in the right...it will tell you how much the speedo etc will be off.
To find tire sizes for the right column, go to tirerack.com or the like and search for tires and available sizes.
http://350zx.com/tire-wheel.html
Chris