FYI when you underdrive anything.You turn it slower...Therefore you are getting rid of the WP cavitation at high rpm.
I don't know anything about the Greddy pulleys. But If I were you find out how much they underdrive them.
When Unorthodox Racing comes out with the RB pulley I'm going to be jumpin on that.
That stock crank pulley is pretty heavy just like the 300zx. And the Z32 saw a lot of power from it.
Check it out:
http://www.unorthodoxracing.com
Look at the Dyno's