I have a #5 Rowell bottom pour ladle that is so big that it's hard to fill it by dipping into my 12" diameter propane tank pot that holds 250#. For consistent weight bottom poured ingots I use a smaller soup ladle to fill it. Still, I think it will work for the new molds.
The #5 is listed as holding 9 pounds of lead. You can actually put ten pounds in one, but it will be so full that spilling molten lead is a problem. The lower weight might work out, though, since each mold filled with a smaller amount will have less width and may fit the SFRB better.
I think for this mold, a high capacity bottom pour processing pot with a valve that can really regulate the outflow volume and pressure would be ideal.