If your talking about the "FG-11" I would say that might bridge a gap somewhat. It might take a bit of ingenuity to fit that gas rig into a plane that was designed with a glow-engine in mind... but overall I think it would be a decent choice if you stuck to the plans as much as you can.

An engine like this would be very economical to run no doubt... and it's well within specs of a recommended four-stroke engine I think. 11cc is right about .61ci.. and in a four-stroke that's just right for a .40 two-stroke replacement. I would do it.

Although do study it, and double check what I'm saying... You'll find what's right for you I'm sure. I really like this size and type of plane with a four-stroke glow engine in about that size range... so I seriously think I'd really like it with a gas rig. This is only my opinion, but if it were me, I'd take a serious look at it... and I do think it's an excellent topic to study and discus.

I'm a big four-stroke fan these days actually. I've found they run very clean, they're very quiet, you can run a bigger prop and have torque to spare, and once set(usually very easy to do) they run forever... so I might be partial lately. Know that there might be a bit more learning curve with the four-stroke engine, as well as the ignition involved, but once learned, you could put an engine like that in anything you want. I hope that makes sense.