Don't make it too hard. The easiest way to check for RF or EMF interference is to build the plane, turn the radio on, start the engine and see what happens.

Seriously, until you do this, you don't know if you'll have interference or not. I have built and flown 3 gas-engine planes: a Giant Stinger with a G-62, a 1/4 scale Dr.1 with a G-38, and my current 1/4 scale Dr.1 with a G-23. I have not experienced any RF interference at any time. I've used both Futaba and Hitec FM radios. I used the standard flywheel ignition, plug wire and resistor plug that came with the engines. None of the servo wiring has any type of choke or interference filter installed. I kept all engine electricals (including the kill switch) in front of the firewall, and all radio electricals behind the firewall. I didn't use any other shielding.

Maybe I'm lucky, but it works and I haven't had any problems.

Dr.1