Use whatever is cheap and easy for you. OEMs do use lead, but steel works just as well, and it is MUCH cheaper. The main concern is that the ballast is properly secured, especially if it is located behind occupants. It would be tragic to be in a survivable crash but be fatally injured by flying weight (it happens). OEMs typically bolt it in (or put it in a box that is bolted in). Seat rails are a good place to secure it. Also remember that the G loads may becoming from any direction. Flight test safely! ��