I bet your slave would work, there isn't much to them inside. A couple of O rings, plunger and a spring. My T5 slave is from a junkyard car, and works fine.
It is direct bolt in but, it still uses the GM roll pin end. So you still have to modify it per JTR, or get the Ron Tyler adapter that Dan suggested. Any GM T5 slave should work.
WOW , looks like a head on crash, and there was a big fire. Not much left of the bike, or people. I'm suprised they didn't cover the bodies with the traffic going by.
You need to measure the space between the frame at the rad support. Some Zs seem to be wider than others. I think 280s are wider than 240s, but measure to make sure.
Did you do a search? There is plenty of info on Z31s
http://www.hybridz.org/phpBB2/viewtopic.php?t=26542&highlight=z31
http://www.hybridz.org/phpBB2/viewtopic.php?t=26328&highlight=z31
http://www.hybridz.org/phpBB2/viewtopic.php?t=25680&highlight=z31
http://www.hybridz.org/phpBB2/viewtopic.php?t=25853&highlight=z31
http://www.hybridz.org/phpBB2/viewtopic.php?t=21573&highlight=z31
http://livethenow.com/tempdir/zcar/v8z/
These are just some of them.
You need to remove the interior, and weld in a bar that goes from one side to the other just behind the front seats. Weld it to the top of the door latch side right under where the 1/4 window starts. This will keep the sides of the car from bowing out. Then check how much of the new roof you have, and where you want to cut the old roof to match it.