RE: Home made weights
The best way to melt the lead is to use a camp stove outdoors to keep fumes that are toxic from you and others. Next best would probably be to use a propane torch. For the shaping part I would line the sand casting with aluminum foil, which will separate from the lead later on. Normally we simply pour the molten lead into spoons or measuring cups of different sizes to get a batch of different weights.
Someone earlier in this thread was amazed that a trailer ball weight was needed in any plane. The Balsa USA Northstar (seaplane) has a rear pylon mounted engine and requires quite a bot of weight in the nose for proper CG. To minmize tha amount of weight, one wants to put the weight as far forward as possible. The best way to do this on this plane is to hollow out the nose cone and pour lead into the cavity. Then whatever amount of weight needs to be removed - not usually much - can be done easily with a drill.