Thanks, everyone. I'll probably grab a Nitto Periscopa (which has sub-2.5" minimum insertion line), but it is good to know that others generally think it will be okay.
Minimum insertion on a quill stem is to assure the wedge is NOT expanding at a point where the steerer is threaded.
Severe damage and failure to the steerer tube can occur.
+1 to rccardr's comments on the amount....2.5" is sufficient.