One issue with a side hinged tailgate is the weight of the tailgate hanging on the bed side. Structurally speaking, the bed sides are not very strong at the back of the truck. They rely on the latched tailgate to tie the sides together for strength.
Not saying it can't be done, just saying to do it right would require some extra support to tie the bed side to the rear bed cross sill.
http://www.mar-k.com/installation_hints.aspx
