I've installed my Z32 kit due to the power I'm now running
I didn't drive many miles with the 6 speed, but it used to change gear okay. I do remember a slight whine so I would point the finger at the input shaft bearing. I might split the bell housing off and check the inside as it's a easy to do
History is also unknown from it's life in Japan. It's been in the UK for a few years, but been in storage on a US base until I bought it