Thanks for all the great comments and sorry to not check in recently. The car that prompted this thread seems to be falling out of the running. Over a week ago I emailed the dealer a detailed but reasonable set of due diligence questions. They sent a polite reply asking for a little time to answer, but that was it until I called at the start of this week. They apologized and said they'd be in touch, but nothing yet. I believe in not forcing things to happen. They know I'm a serious buyer, and whatever the reason that they can't help make the sale happen, so be it.
@jorijori - Yes, I visited Garage Current to see this beautiful 996:
http://www.garagecurrent.com/porsche/996/903/
Actually that visit convinced me that I'm really looking for an air-cooled 911,
but they had nothing in stock in my price range. Seem like a really good shop though.
@black_falcon - I don't disagree with your assessment. That said, the pool of decent air-cooled 911s at "affordable" prices is pretty small here. Buying in the US is an option, but will add about $10,000 (and a couple of months) to ship and get the car on the road here. Considering that, paying a slight premium for a car already in Japan starts to seem more reasonable.