we can’t change the rules, we must engineer around them.
so, why not use the ballast we have (since they’re so heavy), and put one of the battery pack’s cells in a custom bulb.
it could be machined alu. center with heavy metal tips, that thread in. like your maglite flaslights, or simple by using the appropriate sized tube, and silicone-bond (james’ brother), in pre-molded lead shapes.
the pic of wonder keel is a sketch, and is here:
They used to put the batteries in the keels in some of the old solings and 1 meters, I’m told. The keel trunk/fun was thick enough that you could just drop the whole mess in there.
Nice try tho, but I don’t think you could get all 4 cells in there; maybe one of those special 6V or 12V cells maybe. You’d still need a good amount of lead to make up the weight.