Good point on the clutch cover bolt pattern, David, since there are quite a few different bolt patterns and sizes used by clutch manufacturers, some of which won't fit a stock flywheel without redrilling. And this is not a backyard job due to the possibility of screwing up the engine's balance. A new flywheel to match non-OEM bolt patterns can add many hundred dollars to a 'simple' clutch job.
There are special rounded-surface throwout bearings used with some diaphragm clutches. Due to the design, if a normal flat-face throwout is used on a straight-arm diaphragm clutch, you can get a 'catch' in the clutch feel during shifting that bothers some people. The bearing needs to match the clutch type.