That's called lateral balance. I use fishing line under the top hinge of the rudder and on the prop shaft up front. Then I lift the plane by the line and see which way it falls which is usually to the right because of the weight of the muffler. Ill stack lead or coins onto the light wing tip until balanced. How I install the weight depends on the plane and the covering. If I can get away with it, Ill cut away some covering and glue the weight inside to the last rib and fix up the covering.