Hi Simon,
I have been running a spool in my Hara for a couple of months now (using 7-9t mods). I have had no issues with my spool in that time or any other drive train part. My only advice would be to use lots of Tamiya anti wear grease on the spool outdrives and cvd pins along with all of the drive train parts (ie. rear diff outdrives, cvd joints)
I have noticed no chatter from the front end whatsoever, however, I only run about 19 degrees (l/r) steering - measured off a setup station.
Also, you might want to make sure that you use locktite on the grub screws on the spur gear adaptor, and both direct drive pulleys.
Even the standard driveshafts(V.2) have held up with no problems whatsoever.
Hope this helps.
Leonard.