RE: Funtana 90 electric power or a .40 size
You can't think in terms of "what electric motor is equivalent to what glow engine." It doesn't work that way. The glow engine is the entire power system, while the electric motor is only a minor component of an electric power system. You can literally substitute hundreds of different electric motors into a particular electric power system and have the exact same performance.
Without the specifications for the Plettenberg motor, it's impossible to tell what you need out front to get it to spin a reasonably large prop. On a plane like the Funtana, you want to spin the largest prop you can.