Hi John. This was an all-brass tank, 4 ou. With U-shaped wedge, rounded rather than bent outside wedge. I think they may have wanted to have the fewest sharp bends possible because they had a bad habit of cracking on the inboard side where the sharp bends were. Brass is a poor choice for tanks. Nitro fuel eats brass pretty fast. If you purchase a tank with brass tubes these should be replaced from the start with annealed copper. If you find your Darwin tank and are really going to use it watch for leaks or just copy it in tin and copper, using electrical solder-not acid core or silver solder as the flux will spoil your efforts over time.
Dave