They make big ~36" sawzall blades, but the closed cell 4lb (IIRC) stuff was too hard to cut with them according to the installers. They just under wire cup grinders. Last time I did it (on a building) we used an CI cutter, its an attachment for a chainsaw, but they said it was only good on open cell soft stuff.sounds like a used old electric meat knife to carve it down first would be ton faster. Or a heated wire running just long enough to slice down width across one stud to another or maybe even a wire saw for same purpose. Heat maybe not needed?