If it were me making a gas powered version with an engine of that size I think I'd scale up the plans to make the size suit the engine more. A 15 to 20cc gas engine will easily fly a 120" version of the Telemaster and the bigger model will support the added weight of the engine that much better.
The likely issue if you look at the various power plants is that the 15 to 20cc gas engines don't really make any more power than that .70 two stroke glow engine. But they do weigh a lot more. Plus it seems like you're intent on adding more structure to deal with the often higher vibration levels. And that's going to add that much more weight. Your present Telemaster is already over the suggested target weight of 9lbs and you're looking at adding even more with this current plan. So instead why not scale it up to 120" and then it'll be more suitable for a 20cc gas engine. Being larger in every way also means the airframe is automatically stronger so you don't need to beef up as many areas as you are thinking. And the beefing up you still need will be a lot more minor.
At least that's how I'd approach it.