1) This is possible, and you can do it...
2) But you're really better off sticking with the original brakes. If they're the old centerpull brakes, those are FINE. Excellent brakes. The real issue with them is bad levers and cables as OEM equipment, and flexy cable stops on the stem. Replacing the levers with aero levers and using modern housing and inner cables will give you excellent braking. Going all the way and getting another cable stop might help your modulation, too. If you're using sidepulls from the same era, if the bike is anything but the bottom of the barrel, those should be okay, too. Raleigh three-speed type stamped sidepulls ARE pretty bad, though.
Anyway, what you're looking at is a whole lot of painstaking work for less benefit than you think (unless you're planning on using v-brakes, I suppose, but even then...). There is a clamp-on unit with bosses, shaped like an upside-down U. Not cheap, but probably cheaper and easier than brazing.
3) All that being said, I've never been one to back down from a project just because it's unreasonable. If you're set on doing this, go for it! And have fun. Wish I could help you.