Howie..I have no way to test radiation, just 18 years of flying planes with Zenoah engines, from G23s to GT80s, and an occasional Quadra........We started when there were no FM recievers, just ProLine AM systems...Zenoahs have the spark coil mounted on the side of the engine..The wire is solid inside and the plug cap is not shielded...I have never had to use any kind of shielding, either on the wire or on the spark plug...The spark plugs are Champion RCJ7Y....
I must just be lucky...