yes they exist, find a post by someone named nialusa on this celica forum and he has a st-205 (6th gen gt-4) look at his Picture sig....
and no not legal becuase of emmisions, EGR and vairous othe things but you can make them legal with time and lotsa $$$, to tell u the truth its not that hard to get one over, its hard to insure and register it as well as give it an american vin #
and no it woulndt be cost worthey