There was a very recent thread about passing smog with a 3L with headers in this section that discusses this very issue. Typically the visual inspection is not a stringent as it used to be and our cars do not really draw the attention of some other cars that are well know for mods (Mustangs, Hondas, etc) so we seem to be able to get away with more.
Just make sure you run your car for at least a half hour before going to the station to warm your cats and passing smog should not be a problem.
My assumption is that only Turbo cars are going to have a problem with a visual inspection. Ary, have you had to go and re-smog since the turbo was added?