I had the same issue, didnt want to cut up the dash or have a modern look. So for the radio and front speakers I built them into an old ford 3 door heater box. I also have the a/c vents built into the box. It will bolt onto the center of the firewall I had to tear apart the heater and modifed it quite a bit.
For my rear speakers I had to replace the sheetmetal on the back of the cab from the belt line down. When I did that I added some extra vertical stiffeners back there. I was able to use those to with added horizontal brackets to mount some narrow speaker boxes behind the seat.
I added pics of these things in my photo album
http://s1233.photobucket.com/albums/ff392/thirtyniner39/
