My 11-87 will hold 2, 3" waterfowl shells, maybe loaded slugs are longer than loaded shotshells (all shells are measured after firing). Can you remove a little of the lenght of the plug with a knife, saw, grinding wheel, or belt sander or make one out of a dowl? I don't think there is a set lenght for a shotgun plug as long as it does it's job. I would eather make one out of a dowl or shorten the one you have so you can get your two slugs in then check to make sure two 2-3/4" shotshells don't fit (or make sure you don't have any 2-3/4" shells with you, but I don't know the specifics of New Jersey law). Here in CT when I've been checked the warden has only shaken the gun to make sure the plug's in place, they haven't even checked to see how many shells will fit in the magazine.