I usually recommend an airplane of around 1000 square inches of wing area and 10 lbs. as a minimum airplane for gasoline engine use. If you put a heavier gas engine on a smallish plane, you are going to have a heavy, marginal flier on your hands and that's no fun. Check out some of the 72" and up wingspan models offered by Nitroplanes. They have a nice looking model called the CMP Marathon that is designed for 20 to 24cc gas engines. Nitroplanes prices just can't be beat, and I have been happy with a number of their planes. I presently have three of their designs flying gas engines.

http://www.nitroplanes.com/ma20aeairera.html

Good luck,
AV8TOR