go to www.gnttype.org for all the GN/T-type info you need
the option code for a GN is on the options list on the underside of the trunk lid. the code for a GN is WE2. not sure for the t type. also GN's were all black and t types came in a variety of colors. GN's have little grand national emblems on the fenders and trunklid. there are more differences but i cant think of them right now. just go to www.gnttype.org for more info. HTH