I would have to disagree with "too small". With 900 sq. in. of wing, it's fine for a 20cc gasser, and with some attention to detail, an engine like that would offer some pretty "spirited" performance. A decent 20 will have unlimited vertical performance at 10lbs. They say this plane might be closer to 9 lbs.

What I am not sure of is how well the plane is built. For instance many Cubs will be plenty big enough for a 20, but may not be built near strong enough for hard play of any sort. As this is an older design, the design and construction standards are not going to be on par with the latest and greatest from the 3D world where designs are thrashed mercilessly.

Servos would have to be strong enough to hold those big control surfaces, and metal gears highly recommended.

Bottom line, the success of a gas install might depend on your expectations. If looking for a good sport plane, I'd go for it. It should be super. For harder play, I would have more reservations.