Hello gentlemen,
I have a 66 Tempest Convertible and installed my own sound system. You can see it here:
http://www.cardomain.com/ride/388784...ontiac-tempest
for ideas and post or PM me for any details.
My back armrests were already cut by a previous owner, I added the 6x9s to stay standard with the JBL speaker family I was using and to fill the holes that were already cut in.
Like I said on another thread similar to this one, when you sit in the back seat of my car you don't feel like you are at the concert, it sounds and you feel like you are IN the band!!
Enjoy the ride!