Sweet god... my mind is totally blown. I bought a Spicer basic track frame (KHS Flite 100), and have all the parts for my build. I tried setting the race from the cheap headset I had and was very disheartened to find that it would not go on.
I got out the micrometer, and sure enough the fork crown was 27.0 mm wide. This wouldn't be that big a deal if the fork was threaded; Tange still makes JIS threaded headsets. Threadless JIS headsets are another story.
I have searched the internet and found ONE dead ebay auction for a Ritchey WCS threadless headset sized for JIS.
I searched the QBP catalog at my LBS and found nothing...
I'm seriously about ready to just give up and take a file to the fork crown and get the headtube reamed.