Simple heater wire wrapped around the Bing carb can provide enough heat to prevent carb ice. Please note: this installation may not provide enough heat to melt ice that has already formed.
The wire used is glass insulated Nichrome, NiCrA-30DGL, 30 awg, available from www.wiretron.com. Approximately 18" of wire is required per carburetor, with a resistance of just less than 10 ohms, drawing about 20 watts or 1.5 amps and providing about 100F of heat to the carb body.
Wrap the wire around the carb body, avoiding the rubber air filter and any other parts that would melt with heat. Hold it in place with high temperature RTV, and tie wrap the attachment wires where they leave the carbs.
The wires can be led to a switch, or directly to the bus so that carb heat would be available whenever the engine is running.