Good luck. If you do end up running your own speaker wires, just run 'em out of the radio, over to the driver side. Run 'em under the front kick panel, then along under the long plastic strip. From there, run 'em under the rear driver side kick panel, and run the passenger side wire under the back seat, over to the rear pasenger side kick panel, and up to the speaker. I've done this a few times, it's not too hard, it just takes some work, as you have to remove a few interior panels. The bottom of the back seat just pulls up, and requires no tools. The hardest part is getting all of the screws (like for the kicks and the long plastic "threshold") to thread back in.
If I were gonna run new wires to the dash speakers, I'd just feed them into the speaker hole, and find them under the dash, and run 'em to the radio. The door speakers would involve removing the front kicks, and the interior door panel.
'88 GT convertible, 5 speed, 3:08 gears, A9L Mass Air conversion. Mac shorty headers and H-pipe, Magnaflow catback.