Well I thought it was that easy just to buy any 350z or G35 tranny, but this isn't true either
You have to get the cd009 transmission which had better synchros and gears. That came on very specific cars and years.
At this point, I just given up because there are cd008, cd001, cd006 and even 5 speed trannies and all the junk in between... How do you check which tranny? You have to get the vin and run the vin through z1motorsports or someone who has a nissan part number database....
yeah wish it was that easy... BUT if you do end up with a CD009 tranny, then you can get the mazworx adapter and its almost straight bolt on. If you get a z32 5 speed tranny, then that is more like a cut and weld bell housing first then bolt on.... NOT as easy either. All Z32 and CD009 tranny will go into the tunnel.
Here is another tip. If you get a z32 tranny, don't get the one with the bolt on flywheel spacer, that wobbles a little or goes on crooked and you are in a bad situation....
SO down to the question you want answer to. If you get a SR tranny or KA, there are two rebuild kits. One with and one without a reverse synchro. Which one you need? You won't have any idea until you crack it open. Also if have a SR tranny, you also need to source some baulk rings from an xterra as well on top of the KA rebuild kit.
Good luck. I recently did a lot of research on this.... for the rebuild, here is a good reference thread....
http://zilvia.net/f/showthread.php?t=417958&page=2