Hi Sean,
I don't know the road in from Tamworth to Thunderbolts. We have only every come in through Uralla and Walcha. We know Thunderbolts fairly well however (you would join Thunderbolts Way 26 Km before Nowendoc). From there to Gloucester it is a really nice ride although you will find the bitumen is pretty badly maintained in places and you need to take it fairly easy at times. From Gloucester to the Dungog turnoff you take the Bucketts Way which is a nice ride also.
Cheers
Dick