I finally learned what the carb float bowls are mounted to this fuel tank for...

The explanation in the Jan 2012 Hot Rod is that this is a surge tank, and the float bowls control the fuel level in the tank. Fuel from an electric pump is fed into the bowls, and the fuel in the tank then keeps the engine mounted mechanical fuel pump primed. The fuel is gravity fed to the the pump from this surge tank, so it never needs priming during start up. The fittings on top of the tank go to bypass lines from the mechanical pump and barrel valve on the intake.