Retro radio makes a 4x10 Dual voice coil that is a direct rwplacement for the stock 4x10. I used it in my demon with 2 JBL 4 way 6x9's and it sounds great!.
The dual voice coil 4x10 will have substantially better range & bass response than two 3.5" speakers. If I were to build a stock looking audio set up that sounded decent it would be.
2ea: Hertz 6x9 3 way
[ame="http://www.amazon.com/DCX-690-Coaxial-Speakers-Grilles/dp/B0044AFQYW/ref=sr_1_5?s=electronics&ie=UTF8&qid=1353085584&sr=1-5&keywords=hertz+6x9"]Amazon.com: HERTZ DCX 690 6" x 9" 3-Way Coaxial Speakers with Grilles DCX690: Electronics[/ame]
1ea: 10" self amplified & enclosed subwoofer under passenger seat.
[ame="http://www.amazon.com/Infinity-Basslink-200-Watt-10-Inch-Subwoofer/dp/B000063TJY/ref=sr_1_6?ie=UTF8&qid=1353084983&sr=8-6&keywords=10%22+subwoofer+self+amplified"]Amazon.com: Infinity Basslink 200-Watt, Dual 10-Inch Powered Subwoofer System (Black): Car Electronics[/ame]
Running without an external amplifier means spending a couple more bucks on quality speakers with sensitivity rating in the 90's. A setup like this is 1)easy, 2) inexpensive & 3)sounds very respectable