In my limited experience, you should try and fit the ignition moduel as close to the engine as possible (obviously not in the direct line of the exhaust. The battery should be close too, but can be more dicted by CoG needs.

Make sure you use a non-metal pushrod from the throttle to the throttle server. Use a Sullivans plastic pushrod or similar. For my first gasser, I used a metal pushrod and got a brown out on my first landing approach (from the ignition spark being transferred along the metal pushrod back into the server and the resultant voltage spike causing the receiver to re-set. While the plane was fixable, it took me 6 months to get the replacement part I needed for my engine.