Lead blocks, also known as lead ingots, are used as lead ballast when the total ballast weight is high and there are few limitations of space. A combination of lead blocks with casted lead is often used by first filling up the space with lead blocks and after that filling up the gaps between each lead block with lead shot or by casting lead on top of it. In total you'll have a massive block of lead.
Packing Packed on a pallet and sealed with plastic foil. The weight per block is different per lead blocks manufacturer but will be between 25 and 50 kg.