Good afternoon Jeff:
BMWSM (before my WSM!), I grilled many pork butts fairly successfully by cutting the meat into two length-wise slabs where they looked similar to London broils (albeit one with a large bone )! Given the additional heat (from my gas grill) and depending on the original size of the butt, I estimate I probably grilled the meat for approximately half the time I would now smoke the same. If your pork butt is still intact, I would recommend your leaving it as such, using a little patience and allowing the WSM to do its thing! However, if it is already in pieces, you might want to use your WSM, as I do sometimes (like a charcoal grill). Time constraints are generally the same for the meat portions as would be true for any meat grilling exercise found in most, if not all, good grilling/smoking recipe books. Good luck and err on the side of too little cooking unless you are into some of my former grilling products that resembled small, dark, unidentifiable rocks!
?John