Dave--
I just got back on this forum after a two year absence and saw your post...I've got an identical issue with my '73 T/A which I'm trying to get ready for the Bandit Run in May.
The previous owner cut the door panels and installed Sony speakers...I really wish he'd never done so. The challenge with the original lower door panels is the map pockets in the front (which prevent a clean install) and placing them farther back where they are on my car (see photo)
causes interference with the seats (plus the seats block the majority of the sound). I purchased Year One ABS door panels but they require HEAVY modification to fit and the speaker extension is too small to accomodate the oversized grills on my new 6.5" Bostons. I'm not comfortable with the modifications necessary and I've since located a set of nice, used original lower door panels and plan on going back to stock.
I'm also looking into the kick panel solution but am concerned about encroachment into the front driver/passenger foot space and have not yet seen any photos for panels made specifically for the second gens--logic dictates that the emergency brake pedal would cause major interference.
Another option is to install enclosed speakers in the floor of the back seat. I did this on my '76 and am now considering it for the '73...the pluses are good sound and mobility (you can easily unhook the speakers and remove them) but they also eliminate using the backseat passenger floor when in use. Just a thought.
Good luck (and if you come up with any slick solutions, be sure to post).
Best,
Tinman