If you are set on using this shotgun I would say grab a 3 boxes each of 2-3/4" Remington Sluggers, 2-/4" Brenneke KOs and probably Federal Vital-Shok and hit the range and see what you can do with it. I would shoot atleast a box or 2 boxes of each brand with some time between each brand to let the barrel cool. I don't know how well you can absorb slug recoil you you might want to consider a shooting partner to share a shoulder.

Another thing. You say this is a one time hunt so I would think you want to make it count when the moment comes. If you don't have some accuracy or the range you are looking for maybe you can borrow a slug gun from a buddy?