I don't have an answer to your question but I did a search for "carb heat" in the 1/2 VW engine section under the Auto Conversions menu here on the Home Built Airplanes and see lots of discussion threads. I suggest you look over those past threads and see what you find. I suggest you post your question there and also send PM's to those who say they have installed carb heat on their engines. Good luck.
Joe Spencer is the man you need to talk about your 1/2 VW. IF using a Zenith carb most wrap a aluminum oil line around the Y intake tube above the carb to help on the carb ice. But using 2 carbs at the heads like Joe uses, the heat from the heads stops any carb ice and you get more HP. You need to talk to Joe. Joe Spencer is also on this site.
He has some good utube videos.