Thats some clean work...
Just an FYI: there are Dual voice Coil speakers now available out there to get the Stereo output for cars that used to only have a mono speaker setup. Its an option if you don't want to do a whole custom setup like this. Its an easy bolt on and you can choose from 4x10s, 4x8, 6x9, 5x7 or a 6.5"