Wow. If I had a hankering for a vintage touring bike with 650B wheels, I'd just get a late 80's to early 90's steel unsuspended mountain bike. 26" is mighty close to 650B in diameter, and the older MTB would have a few things that a touring bike needs right from the start, at usually a very reasonable cost (Trek 820's go for about $80 here, rockhoppers for $120):
1) lower gearing than a road bike- probably pretty good gearing for touring right out of the box
2) heavy-duty wheels and frame
3) tolerates wider tires, room for fenders
4) long wheelbase
5) canti brakes
Add racks and fenders, change handlebars and maybe shifters and you're good to go! Honestly I couldn't tell the difference between a 650B bike and a converted MTB just by appearance.