Like Chad said Toni Clarke is the place to go and his online catalogue has all the Zenoah goodies listed, including prop/exhaust combinations information. Using a G20 in stock form would most likely only give a marginal flight performance for an aerobatic model like yours having an AUW of 12 lbs, however using the Toni Clarke exhaust system on the G20 which is claimed to give a whopping 40% increase in power would be the way to go.

Karol