Looks like I will have to go this route over the winter as my alloy pulley is now louder than everything else put together.
Quicker than I was expecting - I had it back around 2 1/2 weeks from sending. It's now fitted. Just have to re-check the belt tension as I think it may still be a tad tight.
How did you deal with the customs situation on this? I presume you should only pay duty on the cost of the modification and not the whole value of the modified sprocket. Also you don't want the US company to have to pay duty on the original sprocket, given that it will be re-exported.