Your best bet would be to replace the factory deck with an aftermarket asap. What series JL front speakers did you get? TR? VR? XR? I'm going to assume that the subs you bought for the back are 6W0's. They will fit without any cutting as long as you make a 1/2" MDF spacer ring. There are only 2 problems I see with putting those subs in the sail panels is that those subs are #1 made to be in enclosures, not play free air, & #2 require in the neighborhood of 75 watts RMS in order to drive them properly. Even changing out the headunit to an aftermarket piece would net you only 18-22 watts RMS on its best day. (Don't believe the 50x4, 55x4, 60x4...just inflated numbers made to inflate sales.) So, IMO, to get the best sound outta those JL's, you'll need to enclose the 6W0's & get a small amplifier on them.