OK. I'll go measure it. It was 400 Lbs on the scale at the metal recycler. I was at the office when I posted yesterday. Not with the block in front of me.I am questioning the weight of your block of lead.
A cubic foot of lead weighs 708 pounds. That would 12"X12"x12".
If your block is 18"X18" x18" it would weigh well over 1000 pounds.
BTW, Great haul.
I would go with melting it with a weed burner or some other heat source.
Bruce