scarlson 

Just a word of warning, this stem comes in two bar clamp diameters: 26.0 and 26.4. The 26.4 is proprietary Cinelli clamp diameter so you'd need to find Cinelli (or other compatible Italian) bars. Those Nitto bars are either 25.4 or 26.0. Just pay attention to what you're buying or you'll end up with a stem that doesn't fit your bars!! I would suggest a Nitto Crystem or Nitto Dynamic if you can't find the Cinelli XA in the right length with the proper clamp diameter. They have a little of the Cinelli XA look but without the hassle.

It's also less hassle to use a drum brake on the rear, and you probably won't notice the difference in braking power on the rear, and the "rear-drum, front-disc" combo is something many motorcycles and cars did for some time, but it sounds like you've got your heart set on disc brakes. I'm interested to see the fabrication and brazing job! I do little things to old frames sometimes too.