I believe the only GN that was carburated was the 82 model, 78-83 Turbo regals are rare pieces and nice cars, not to much much of performance compared to the 86-87 models but good performance for there era.
How well they perform depends on your point of view. Mine runs 15's and they are some big bugs still to work out. Compared to a 86/87, that's slow. Compared to a non-turbo V6 which runs 19's, or the average ricer-modile, that light speed.
Like any car, they will pass emissions just fine if they are running well.