You may find that successfully silver brazing a small boiler can be a somewhat complex affair. Correctly identifying the best burner, or even one that is, as you write, "suitable", often interacts with other factors, such as the arrangement for entrapping heat with refractory material, the use of supplementary heat, and the alloys and technique used. The burner head in your picture is one that seems to be commonly used in weed burning, and in heat shrink applications. It might well be suitable for your purposes, but in the absence of information about heat output, flame size and shape, and so on it is hard to be sure. "Airco" doesn't narrow things down much. They make dozens of burner tips for many applications.