You can use 1/4 oz weights sold at almost any hobby store ... but for latteral ballancing, I've never really needed any more than a couple pennys and a couple drops of CA or superglue. Start with a penny on the wing tip. If it's too heavy, slide it in toward the fuse till it ballances out and glue it to the bottom of the wing. It might not be as bad as you think though. The torque of the engine should counter the muffler weight. Any latteral ballancing should be done before the engine is installed.