flylow,

The gasser I have in mine is a 21cc Echo. This engine is lighter than the 31cc you have. It also does not have as much power. The Ryobi has a rear carb, which will complicate an installation. You could give it a try ... why not? Do shorten up the nose to compensate for the heavy engine. I think you can shorten it more than the 3 inches I did without a problem.

Good luck,

BP