Great Planes is conservative with their engine recommendations because guys try to claim a structure malfuction under warranty when they bolt a larger engine on the front. That is just Great Plane's defense. So if you want to go larger just make sure the firewall is well glued any maybe add some tri-stock and/or fiberglass cloth. Just be sure it is WELL GLUED. I guess this is a kit so you are doing the gluing anyway.

I would think a Saito .82 or even their .91 would be a nice power source for this model. With the .91 you would probably need a 15x4 prop for 3D so make sure the ground clearance of a 15" prop is enough for you.

I should add....... to prevent aileron flutter you should upgrade to 4-40 control rods between the wings and be sure to seal any gaps. There have been some complaints about flutter with this model. Some guys have criticized me for providing this recommendation, but if I am going to express my opinion that it is OK to go with a higher than "allowed" engine I am going to say go heavy duty to fix a possible problem area that could end your project in a hurry........... Good luck.