I installed a Kenwood stereo into my Shelby GT 500 center console using existing holes to run wiring and built a speaker box that goes directly behind the fold up seat. Wiring to the speakers are on a plug so it can be quickly detached and pulled out in seconds when at a car show. When left in it is hardly noticed. Make sure the stereo you get is short enough to fit in console. The plate is made of MDF (medium density fiber board) painted black then wrapped in speaker grille. The speaker box is under here in the front of the trunk. The box is also built out of MDF painted black and also wrapped in speaker grille. The wiring was routed under the carpet with no holes cut. Here are a few other photos of the car.
That's a very nice car, congrats! I went a different route, I had an MP3 plug istalled into the back of my original AM/8-Track unit, and then ran some rear speaker wires similar to where you did to a removable box like yours. The old unit has the ummphh to drive the rear speakers, and the MP3 cable is stuck back through the glove-box light hole (it is stored in the glove -box along with the XM radio unit and MP3 player) when not in use at shows and for that orginal look even when you open the glove-box.
Very impressive!!! I like both ideas. I need to figure out what I want to do with 6S2388. It is a continuation GT350 and they installed a POS system in it when built it in the early 1980's. I want togo back to the basics but have modern sound. Randall