Send it to Howell, they bore at 55mm which is good and solid and they've dyno tested it as the best bore for NT. I have a spare TB if you'd like to buy it and send it off then sell yours when it comes back in. $35 shipped, email me.
ARD is backed up a bit I think last time I heard from them... they did mine in no time flat a long time ago... but i guess they're either busy or sitting on their butts lately..