I got the small lead ingots I ordered online. 10 pounds of lead in a small cardboard box one third of a shoebox. Shipping litterally cost as much as the content itself.
Each ingot is in the 300-380g range (3/4 lb). That's about 2.8kg (6lb) of ballast not counting the battery pack !
Test shows that it might actually take an extra ingot closer to the bow ...
Once the amount of ballast is OK, lead ingots will be coated with G4 marine primer, as lead is highly toxic. Thanks to hook & loop ballast location will be adjustable.