The schematic: http://forum.allaboutcircuits.com/attachment.php?attachmentid=37289&stc=1&d=1322976657 -- has been updated. Wrong crystal value shown and there is now a base resistor to aid with turn-off.You should also add a base return resistor to speed the turn-off of Q1.
When you say base return, do you mean emitter to base? I agree that this would help switch it off much quicker, but pretty sure that it would cause chaos with the DAC. The Sync line would be providing a path to forward bias Q1.
Could go a bit lower on the 47K I guess. What are your thoughts?