Update:
After returning to BB to look for a speaker box I talked to the install guy. He was adamant about the rears are running off the jvc head unit, the doors and fronts share a common ground and are running off the 4x40watt P-amp. If that is the best the P-amp can do, then I have to rate it garbage, or maybe flea market worthy.
I picked up a pair of 3 1/2" infinity ref 3022cf to see how they fit. They were returned once, looked fine and after BB 10% discount they came to $72 OTD.

Talk about bending over and taking it!! Amazon has them $33 with free shipping.
http://www.amazon.com/gp/product/B000MPIWHG
I would love to hear what the Kappas sound like before I buy the ref. ref=3 ohms, kappas=2 ohms.
Ok the scoop, they will definately fit in the current bracket(with one little mod as they have a small square piece on the side. I just need to notch out that on the stock harness. I actually could fit two just like factory.
Sound: They were by no means as good as the 4x6 kappa. They had a little more tinny sound. Not horrible, as I could adjust the fade and they harmonized with the fronts real well.
Question: What would you guys/gals do? 1 or 2 speakers on each side? I am going to do a search to see if there are any Kappas in 3 1/2. 4 inch just wouldn't fit quite right. I really would like to have them secure, safe and stock looking.
Found Kappa 32.9 for $55 a pair or x 2 for $110.
http://www.amazon.com/Infinity-329CF-Custom-Two-Way-Speakers/dp/B0018SJ4AK/ref=sr_1_1?ie=UTF8&s=electronics&qid=1250204702&sr=1-1