Putting the lead into the keel took a long time. I poured in batches of about 8 kilos (about a pint of liquid), because that is what the gas burner could deal with. I had to cut chunks off the lead flashing that would fit into the pot. A wooden spoon (a strip of plywood) was very handy to stir things around and remove the dross, although it got a bit shorter after each batch.
As you can see in one of the photos, I used a few 2x4s as blocks to keep things together. After every second pour, I moved the blocking upwards by an inch or two. This worked perfectly and everything is just fine. Unless someone will be dropping in a very large amount of molten metal, the recommended use of pavers, bricks, etc. is probably an overkill. However, please don’t blame me if the 2x4s fail to work for you.