Sooooo. Turns out the customs delay was caused by Tirerack not sending the right paperwork. Once this came through and after a fee for duty and an $89 quarantine inspection fee I had my new tyres in my hot little hands!
Overall, still shitloads cheaper than buying here and the tyre guys that fitted my new semis to my TE37s looked suitably in awe when we turned up there today.
This is a very welcome sight in my lounge and will be even more welcome on the GTR when she comes home soon:
Over all, experience with Tirerack was awesome!