reading through that thread you posted, seems that there are some other options to really consider.
someone posted towards the end about using a rb25 flywheel. the light weight ones of those are like 12 pounds. pretty sure they are even bigger than the d21 truck ones. if they are bigger, then that would let you run the bigger clutches like the 300zx or the 350z clutches. you could get away with a stock clutch. or something very similar to it and not have to worry about it being able to take a beating, and it should last a long time.
The higher the stage of a clutch, the faster it will die off. So by the time you get a 240sx clutch that can hold 500+ horsepower, you're looking at replacing your clutch pretty much every year. But if you did a stock 300zx clutch, while it can hold 300 or so, that is rated for a car that is 1,000 pounds heavier.I have no doubt that it would be able to hold back 500 hp in a 240. The added perk there is that you can get anywhere from 60k to 100k miles on a stock clutch.

It is this sort of stuff that makes me really miss my 240's... I don't know of any white bunny type thing for the 300zx's...