I did a build with one of those cars with 2 VFL 12's off a shredder, back in the day. Really easy car to do sub forward build in, nice square opening.
I don't recall the details but I ran it to pretty much max dimensions..probably about 4.5 - 5 cubes gross with a center port around 95-115" of port. Removed the from seats and it slid right in the hole.
Metered mid 148's sealed on the dash and was somewhat musical....(take that with a grain of salt, I don't think I've ever tuned a box below 45hz)