Thanks everyone. I took it out for a 10 mile spin today--I like the stable, comfortable ride.
I found this with a little info on Tange 2001. It confirms it was a simple alloy tubing that was thicker than most--geared toward supporting a 200 pound rider, which I suppose would make it a good choice for a dedicated touring bike.
http://www.desperadocycles.com/Lowdown_On_Tubing.html
I'm guessing it's 1981--83ish, given the Deore group.