The thing to look for for interference is not the receiver location as much as the closest any component connected to the receiver is to the ignition. Servos in the motor box is asking for trouble. I know that lots of people get away with it, but I've also seen lots that didn't.

I put servos in the motor box, but I optically isolate them by at least 12 inches from the ignition. One day I wondered just how necessary that was. After all, I was using a PCM receiver, the DA ignition is very well shielded, and my receiver was nearly three feet from the ignition. So I removed the isolators and connected the servos directly to the receiver. My ground range check went from 300' to about 100'. That was all the proof of interference I needed.

I agree with going PCM. For 10 years I flew half of my planes on PCM and half of them on FM. I've never had an FM receiver that didn't glitch at least rarely. I've never had a PCM receiver for which I've had any kind of a glitch at all. I figured 10 years was enough testing, and now everything I fly is PCM.