Jeff,
A standard DIN stereo will fit into the dash w/o a adapter plate. As for which head unit, I went with a Sony Explode MP3 player. This aliviates(sp) the cockpit of loose discs and frees your feet of a CD case. Having 160 songs on a single disc is worth the 15 minutes it takes to rip some MP3's and burn them to a disc. This head unit also plays standard CD's. As for the 6" mid-range speakers in the back panel, JL audio makes a 6" sub that will fit into the stock enclosure. Be warned; however, that the stock backpanel is far from air-tight and makes a lousy enclosure for subs. The 6" JL's are not the most powerful option either. For my Viper, I had the back panel removed, a custom box crafted and recasted the entire piece in fiberglass with a 10" JL W3 incorporated. It is a little expensive(~$1000), but the sound is well worth the trouble. I also went with a set of MB Quart components to replace the standard speakers and tweeters in the doors. The stock amps are also weak and do not reproduce the cleanest signal. I went with a 3 channel Xtant mirror finish amp that I has been custom installed in the trunk. The only drawback was I had to loose the spare tire, not that I would use it anyways. I hope this helps you out, if you have any other questions, don't hesitate to drop me a line.
-Leaf
