Measure from the leading edge back to the trailing edge. Then set your cg at 25% of that measurement back from the leading edge. You may want it just a tad nose heavy at that setting. Nose heavy Planes are much easier to control than a tail heavy one. That should get you close enough to do some test flying. Then you can tweak the cg based on how it flys. Sorry I don't know the exact C.G, but someone might show up in here yet that knows exactly what Plane it is, and where the cg should be.