Definitely synchro's. Stock T56's aren't too hard to destroy, if you take care of it though it'll be fine. They arent too hard to rebuild either, but i dont know anything about doing it for the vette, im sure its the same though. Taking it out is going to be a bitch, prepare to drop the whole rear subframe/end/axles/tires/rear suspension/torque tube. Oh it is going to be a major bitch, so when you do it, dont cheap out, replace everything you can so you'll never have to do it again, put a new clutch in it and definitely a new slave cylinder, since theyre inside the bellhousing if it goes out it means you gotta do all the forementioned stuff again to replace a >$100 part. While you're down there you might aswell put in a remote bleeder too, and fuck it, throw some 4.10's in the rear end. Also replace the rear main seal as those leak quite commonly. Also do new trans mount n bushing and stuff. I'd expect to spend no less than 2k for maintenance and something that doesnt make the car a whole lot faster. You'll love LSx power though.