hi XXXXXXXXXXXXX,
there are the 3 main screws that you mentioned, but you will also need to remove the emergency flasher button there is 1 screw that go'es though the center of the switch.after you unhook the harness under the dash there is a clip on the steering coulum that the harness clips to. after the clip is released you will need to bend the wires so the conector is in line with the steering colum, after this is done you will be able to remove the switch.
Chevy Mechanic
ten years working on g.m. cars of all makes