If you're planning on removing the original radio, you better check with the dealer first. GM cleverly designed in some tricks to prevent you from removing it. When it malfunctions, you are locked in to one of their two grossly-overpriced repair centers. They stopped allowing us to buy radio service manuals after the '94 models so they could lock up all the repair business. To prevent you from buying a less expensive replacement radio, they started building the Body Computers into them on some models as far back as 2002. To combat that, the aftermarket industry came up with a "radio relocation" kit that allows you to mount the radio somewhere else so the engine will run and other stuff will work. You just snip the speaker wires and run them to your new radio.
This doesn't apply to all GM models but you want to know for sure before you start cutting wires and get a nasty an expensive surprise.