Ray, by balancing laterally you are hanging the airplane by string tied to the propeller shaft and the fin, right? And you have the strings moved so that they're on the centerline of the airplane? If it is tilting to wards the muffler, let's make sure that the muffler is the problem first. Take off the muffler and see what happens. if the plane still tilts the same way it's not just the muff. Instead of stick on weights get some small gage buckshot and drill a hole in the solid wing tip. add the shot to the wing tip till the plane balances with the muffler on then fill the hole with glue. Once dry cover the hole with a monocoat patch.

HTH
Tom