I used an antique fire extinguisher as the overflow tank for my 1928 AB Canopy Express (Justin). I cut up an old electric motor mount to use as the overflow tank's brackets.
The inlet tube is clamped to the radiator overflow tube and goes into the tank from the bottom. There is also an overflow tube for the overflow tank ;-) that comes out the back side and is around 1 1/2 inches from the top. That tube is open to the ground, but has never 'puked'. Even driving at high elevation (7900 feet) in 98 degree heat.
What's not in the pic is the sheet metal heat shield that I put over the exhaust pipe so the radiant heat would not affect the overflow tank. That was added later based on a hunch, not clear evidence that it was needed.
