I have both magneto and EI Zenoahs. I have found the only challenge in working with the converted engine is the placement of the battery and mounting of the switch just as you have mentioned. I found that using a square 4.8v instead of the flat 4.8v seems to simplify battery mounting problems especially if you are putting the battery in front of the firewall mounted to the engine box or firewall. It's just easier to place a square battery and secure it. I like to use those cool little velcro cable ties with the battery wrapped in foam. Just something I have done to make things easier for me.

The switch can be mounted to the cowl or just aft of the firewall. I've never had a interference problem and I think that is because I follow that rule. Keep the switches as far apart as possible and also radio gear from the engine. I own controlling stock in RCIGNITIONS and have had nothing but good experiences. My newest converted G62 has been rumored to be 12 hours away at the moment . Now if I can just talk Ralph into anodizing these engines blue or red so they will run better. Note to self... DUCK!!!!