Whoa... 8" rocks!  

  (I won't be dropping my tiller off at your place anytime soon..)
I've got a John Deere 660 tiller.  Forward rotation and slip clutch.  It's stored outside on a pallet and double tarped.  Never a problem with the slip clutch.  I think the clutch is a better safety feature and helps to avoid more costly damages whenever you encounter situations that are unforeseen; like 12' of buried 3/8" chain!  (Maybe that's worse than an 8" rock..)
Interesting info regarding the advantages of a reverse tiller.  My next tiller could very well be a reverse machine.
AKfish