The fork and release bearing sound like they are ok if the pressure plate is fine, the way the clutch plate failed sounds like its been over worked more than anything else. If its a standard plate on a modded car with an LSD then its not going to be up to the job. Before the diff the clutch only had to hold the load of 1 tyre before it would spin up, now it has to hold the grip of 2, its under a bit more pressure.
I have seen the slave cylinders stick out as well as in, so its as if the clutch pedal is being ridden. It causes friction plates to wear out and wears the pressure plate over time, its usually from dirt in the system and a fluid change sorts it. Your mates failure sounds like he is giving loads of beans through every gear and from a standing start. Its usually from dirt in the system and a fluid change sorts it.