We flew radio assist old timers in contests for years using McCoys, Anderson Spitfires, Super Cykes, ETC...Points ignition, Kraft and Proline AM radios...The spark plug wires just clipped on the top of the spark plug...We put a small resistor in the lead, right at the plug..Worked fine, I could get the plane so far away it took a helper with binoculars to see it to be able to keep it under control...With the new shielded plug caps from C&H on the 1/4-32 Rimfire plugs there would be no problem with RF...Problem with these would be fitting the 6 oz of ignition and battery in a small airplane....
Fuel is not a factor, but it takes more oil if you use gas....