^ Correct you can look up part numbers for correct spotlights and installation kits there.
For a 2008 Chevrolet Tahoe we have two different mounting locations available: Door & Inside Post. Door mounts through the frame of the door and is easier of the two installations, Inside Post the bracket is mounted on the inside of the vehicle instead of the outside and goes through the post, but will need a small notch made in the door. It is much more complicated install, but is often considered to look more professional.
Door Mount Application: Spotlight with a GM length shaft mounted with a 254 installation kit for driver side. Not recommended for vehicles with side air curtain.
Inside Post Mount Application: 206000 Series LH Spotlight mounted with a 257 Installation kit for driver side mount.