Hey thanks dude, I'll check into this Z specialties thing, but I'm attempting to create my own bass box for my Z with one aimed towards the windshield the other straight up, then throw the 6x9's in those little glove compartments behind the seats. If I can show you my ideas, or if I can find better ideas through friends I'll let you know.
Had speakers that way when I bought my 72. Can't really describe it other than even when cranked could never really hear the stereo right. Bought the MSA box and the sound is much, much better now although lacking somewhat in the low frequency range. Perhaps a sub in the wheel well would help.
If you put 6x9's in those compartments behind the seats it will throw the sound staight up. I have the 6x9 box for the back panel it sounds great. The sound goes towards the front of the car. Also you don't need two subs, one 12 or even one 10 will be fine. In such a small car as the Z you don't need a lot of bass to be able to feel and hear it. By the way you can get the 6x9 box for 149.99 from motorsport 1-800-633-6331