i believe a pistol grip equipped s-12 is a no-no in jersey ... but not a thumbhole stock.
here is a conversion kit:
http://www.mississip...tock-p-912.html
i have one of these on an ar-15. its really nice. dual bungee and thick nylon straps.
http://www.northeasttactical.com/joomla/index.php?option=com_content&view=article&id=49&Itemid=58