I was not bright enough to take pictures of the install in the '76 280C but I'll try to explain what I did.
In the front, I made new kick panels that replaced the existing cardboard and carpet panels. By layering 3 pieces of 3/4" MDF, I got enough depth to mount a set of 2 way components and their crossover. The outer layer was full size and the two inner layers were only an inch or two around the perimeter to get more volume. The whole thing was covered by a fiberglass panel that was covered in acoustically transparent cloth so that they ended up pretty much invisible. I did have to take out a mounting bolt for the parking brake pedal so that it could swing inboard to clear the left hand enclosure.
In the rear, I applied 3 layers of fiberglass over the sound deadening tar stuff to encapsulate it as it was breaking up. I did cut the openings to install 6X9's but from what I understand you may not be able to do that.
I built a 10" deathbox from plans,
http://www.decware.com/dbk10.htm I didn't want a window rattler but did want good clean bass.
The four corners were powered by a 45WPC Alpine amp and the sub by a 100W bridged amp.
That car freakin rocked! As it well should, what with the electronics costing $1000 more than I paid for the car.
On another install I tried building rings to mount speakers from the underside. Sort of looked like tunnels from the topside. Sounded so bad I never bothered to listen to it again.
You will never get any bass out of dash mounted speakers unless you can build correctly sized enclosures behind them and that is nearly impossible in an existing car. If the stamped recess in the rear is shallow, you will never get any bass out of the rears either. Speakers have to have the proper amount of enclosed space behind them and the sound waves from the back side can not be allowed back around to the front side. This will cause cancellation and is sort of how Bose noise canceling headphones work.
I have heard of folks putting a sub in the trunk, "venting" the floor of the first aid compartment and propping the lid open a smidgen.
Michael
Forgot this link,
http://www.crutchfield.com/c_3/Car-Audio-Video.htmlThey may not ship overseas but they do a good job with providing specs including mounting depth.