You said it yourself, 'The G-Trick is designed for an YS91' .
You will be adding 300grams to the front, so another 300 to the back to balance, plus a bit of extra glue here and there because I hear of quality issues. So, even by being generous, we are adding roughy 400grams to a feuled plane with a YS 91. If you want to put a gasser in something, look for something that is designed for a gasser. I hear all the time of people who say that they used to put big gas engines in all their planes, and thought it flew wonderfull. They then replaced it with a smaller, lighter glow, and it is just a whole new plane, alot better at everything!
But at the end, I suppose whatever makes you happy!
Rob.