for a cat that is mouthy, I have found that saying "OW" in a meow like
fashion (high pitched) is more effective.  When they are still with their
siblings and they are too mouthy, their siblings will meow at them to stop.
When you have an excessive biter, the siblings will meow, then completely
ignore their sibling.  No good or bad attention, no attention at all.  When
the aggressive kitten won't listen, the mother will often pin the kitten to
the ground (ignoring it as she does) to show him that the behavior is not
acceptable.

Also, scheduling play time with items that are appropriate for him to chew
on will help as well.  Fishing pole type toys with soft toys on the ends are
very helpful.

Good luck with the new kitty.