The best way I've found to find the balance point quite accurately is to make up a long loop of string that hangs from a hook in the middle of the loop so each end supports the model around the fuselage in front of and behind the wing. The model then hangs like a pendulum so the CG is directly under the hook. Adjust the model in the string cradle so the fuselage and wings are level. Hang another piece of string with something like a pointed fishing sinker from the same hook and it'll point directly at the CG. While it's hanging you can add weights wherever you like to move the CG to where you need it before sticking them on.