I have cut a large piece of 12-14 BHN lead up. It was a 2'x1' by however thick to add up to 107 lbs. I placed it on 2x4's on top of one of those cheap blue plastic tarps that they used to give away at Harbor Freight. I used a Sawsall with a wood cutting blade. The tarp collects the crumbs. I cut it up enough to fit in a cast iron dutch oven smelting pot. I tried an axe and chisel first. The Sawsall worked, not easy, but worked.
If I was you I would look for a big enough smelting pot and melt it all at once, pouring it into ingots.