What do you guess the aprox diamentions

6.86" !?!? That's pretty accurate for a guestimate. You are probably thinking that the speakers are JL's 6w0 subs. If that's true then your dimensions can't be used unless one of the speakers is acting as a diaphragm or they are different speakers.

We're pretty sure that the car is a Mazda RX-7 from the looks of the body and center console. Probably from mid to late 90's model. If that's true, then what we are thinking is that those are just side boards for an open air (infinite baffle) setup. The speakers would have to be JL's 6IB0 (or 6IB2 or IB4). Those were made as a specialty woofers only and according to JL, it seems that it is discontinued now in America. They look identical to the 6W's. Europe seems to have them on many of their

As per your dimesions, even if they are the 6W0's, the box is way too small (half the recommended minimum size) to make it effective unless 1 sub is inactive. We took into account the shape of the box is larger at the bottom (even pushing 9"), but still only meet the requirements of only one speaker (and half of the other).

In short, we do not believe it is even a box to begin with. It would make more sense to use those sides as support for an open air sub setup using the IB speakers.