How did I miss this thread?
I would use the Shiva, and make a new box if you are able. It would cost less than a new driver. For a 12" 1.25cu foot is about as small as you are going to get. There are some good 10" drivers that work in about 0.5cu ft, but IMO it is not worth it.
I have a 12" that will go in my IS300 some day. I do not yet know how I will do it, though. I was thinking either make a custom enclosure in one of the far back corners, as I have seen a few contour people do, specifically Trapps. Or, I thought about a false wall behind the rear seat. Since the back seat does not fold down anyway and the hump on the floor, I thought it would take up the least amount of useable space, at least the space that I generally use. Colin has just recently done this with his SVT using the same Lambda PB12 LE driver I have, although I will make my box a little smaller than his 2.0 cu ft.
