Trevor,
On my 67, I have a Jensen 600 watt amp under the driver seat(picture below). It just barely fits. I have a Sony MP3 connected to the low power inputs. There's a speaker in each kick panel. I have the templates to cut the holes in the same place they were cut at the factory. Just let me know if you need a copy. I used welting to cover the rough edge where I cut the hole. You can also buy the factory style speaker covers from Classic Industries. I didn't want to spend the money on them(yet). I made two speaker boxes for the 6x9's in the rear of the car. I made them as small as I could for the 6x9's and I leave them on the floor in back. This is an excellent sounding system. I find it priceless to have perfect stereo separation between the front and back and side to side. Some tunes really take advantage of the four channels and sound awesome. Jethro Tull, Locomotive(breath) is one.

In the 69, I have the Hidden Audio in the trunk. It's AM/FM stereo and has a 10 disc CD changer. It has a small display that I mounted under the dash. It also has a remote with all the functions. There's only two speakers in that car because I didn't want to cut the original kicks(numbers matching car). I believe it's 118 watts per channel or so and it's almost as loud as the 600 watt set-up in the 67. I think both are a great choice but the 600amp-mp3-4 speakers is, by far, better sound, better selection, louder and better hidden.