The crucible goes on the stove with enough lead wheel weights inside sufficient for the pour. Begin the pour as soon as the lead is molten. Take your time and be very careful with the pour, but it must be done all at once. Overfill the hole in the rudder blade somewhat to allow for shrinkage on cooling. Shut off the stove and walk away from the job for a few hours.
Lead stays very hot long after it has solidified.
If the weight gets loose in the blade due to shrinkage, you can tighten it by placing the weight over an anvil and hitting the lead with a hammer. That squeezes the center and expands the perimeter. Laminate this exactly as you did the rudder blade. A block of hard rubber or phenolic plastic bolted in place might be best. Make it too long and shorten it later if needed.