Well, they are not stock. They look rougher than my GTS headers. Mine may have been repops. They did not have the tooling marks in the tubes like yours do.
They maybe original factory gts headers by the original vendor? They are definitely tri-y's.
As such they are giving away about 30hp on the top end but provide more low end torque off of idle.
They work best on a basically stock engine. They do not work well on a high performance/race engine.