>David, on the subject of clutch repairs, how thick should the >surface  be?
  Or to put it another way, how thin should it be >before you replace the
disk?

If you have the engine out, replace the clutch disk even if it looks like
it's new.  For the 15 or 20 bucks you'll spend it'll be well worth it.  If
you don't do it now, you will regret it soon.  I always replace my pilot
bearing anytime I have the engine out.  It costs about 5 bucks.