If I remember well, Charles has already given this suggestion on some other posting in this Forum and I agreed entirely with him.
DON'T weld anything on the crane boom or counterweight without having asked first for the manufacturer's instructions.
If you make a weld and something goes wrong (Murphy's law !!), the responsibility will be all yours. A crane boom weld that brokes can cause a disaster.
Giovanni S. Crisi
Sao Paulo - Brazil